I will go into more detail about the aspects of the mod event by event

Event in which large states will threaten other states to convert or be converted by force or try to persuade neighbors to convert.

Initial Event:
Event fires if a state is 5 times larger in total development and 3 times larger in military power then a neighbor state and they have different religions. The potential target cannot have just changes religions (has conversion zeal or a similar modifier) and must be an independent nation, not a subject.
The event randomly chooses a target state if there are multiple possible states that meet the requirements.
The event will display options for threaten or convince depending on whether or not the states are allied and have good or bad relations, the actual function of the event is identical. A state can also choose not to take any action.
AI choice is weighted by AI personality where AI militant leaders are more likely to threaten rather than take no action etc.
Once the choice is made, an event fires for the target which allows the target to choose how to respond.

Target Response:
Threatened states must choose whether to convert and improve their relationship with the larger state in an attempt to defray tension or rebuke the threat and face the possibility of war. States weigh a number of factors but the baseline is a calculation of relative power.

The target state uses an average of the ratios of total development and military power and the technology group gap between it and the threat initiating state.
Ratio for total development uses a set of variables to record the total development of each state and then divides to create the ratio.
Ratio for military power uses the military_strength condition in the vanilla code.
Tech group gap value first assigns a value to a variable associated with each tech group based on the tech development bonus/offset where western tech group reads as 26, eastern as 24 (20% less at 10% per ‘point’) etc. We then subtract the threatened country’s tech variable from the threat initiator country’s and square the difference.

The three final values are then added together and then the sum is divided by 3. The quotient is a positive number (usually between 1 and 100, although it can be higher in some cases). The higher the number, the larger the gap in power between the two states.

This value is then directly applied to form the base of the AI Chance. If the final value is a 20 then the threatened state has a base 20% chance to choose the accept the demand to convert option and a base 80% to refuse. At a value of 60 the state has a base 60% chance to convert and a 40% chance to refuse. The event parses these out in 5% increments.

The decision to accept the demand is further modified by:
The target’s current religion where orthodox, Coptic, Jewish and Zoroastrian are 80% less likely; Muslims are 70% less likely; Confucian and Shinto are 30% less likely, Protestant and Reformed are 10% and Pagan faiths are 50% more likely.
Religious Unity where higher degrees of religious unity make the target less likely to accept and lower levels more likely
Prestige where higher levels of prestige make the target less likely to accept and lower levels more likely
The presence of religious nationalism makes the target 40% less likely to accept
If the two nations are from different religious groups then the target is 5% less likely to accept.
These additional modifiers are only applied to the chance to accept the demand, not to the chance to refuse the demands.

Once the choice is made:
If the target country accepts it will change state religion. The target’s capital will convert to the new religion. Various religious modifiers to prevent conversion to a new faith and assist in converting heretics are applied. The threat initiating country gains a significantly better opinion of the target country. The target country gets a negative relations modifier towards the threat initiator.
If the target refuses to convert, then both countries get negative relations impact and the threat initiator gets a CB on target.

Event in which Smaller understand their precarious situation when faced with larger neighbors who follow a different religion. They have the opportunity to try and appease their neighbors by converting to their faith.

Event uses the same power ratio criteria as the large state event (small state must be 5x smaller then large state in total development and 3x smaller in military power)
The event picks a country if there are multiple options.

The event then calculates relative power using the same formula as the large state event.
The small state will make a choice about whether or not to reach out to the large state and propose to convert to the large state’s religion based on the same base power ratio.

However the small state choice is modified one additional factors:
The state is 70% less likely to attempt to convert and appease the larger state if it is in the Christian group and the other state is in the Muslim group (and vice versa)

Event where a nation has poor relations with its neighbors despite sharing the same faith they will sometimes choose to change the political dynamic by elevating a minority religion and try to forge ties with other nearby nations of the same new religion.

This event is intended to simulate a situation in which a nation is bullied by its slightly larger neighbors, fears for its safety and decides to take up a new religion in order to win new allies and security.

Event fires if a nation has a significant minority religion, is not a tribe or steppe horde, has a neighbor or neighbors who are about 2x as large (total development) and militarily stronger but not quite 3x as large and 3x as strong. The neighbors must be the same religion as the initial nation and have poor relations.

The event will pick a religion to potentially convert to if there are more than one contender.

The state has a base 30% chance to convert and 70% chance to refuse to convert

The decision to accept the demand is further modified by:
The state’s current religion where orthodox, Coptic, Jewish and Zoroastrian are 80% less likely; Muslims are 70% less likely; Confucian and Shinto are 30% less likely, Protestant and Reformed are 10% and Pagan faiths are 50% more likely.
Religious Unity where higher degrees of religious unity make the state less likely to accept and lower levels more likely
Stability where higher levels make the state more likely to accept and lower levels less likely
The presence of religious nationalism makes the target 40% less likely to accept
Government where republics are more willing to change religion and celestial empire and theocracies are less willing
The state is more likely to convert if there are more than 1 neighbor who has the same religion is slightly larger and more powerful and has bad relations
The state is more likely to convert if it has a neighbor who is not quite as powerful as it is but with whom it is allied
The state is more likely to stay with its original religion if it has a neighbor of the same religion, at least as powerful, with whom it is allied.

Even where a state in certain threatened circumstances can adopt religious nationalism, making their faith identity part of their nation identity.

This will make it harder for other states to threaten them with religion and give them bonuses to repel invaders.

Event will fire if a state does not have any neighbors who share its religion and at least 80% of its power and with whom it is allied. The state must have one or more neighbors who are stronger than it and of different religions and have poor relations with them

The state has a base 30% chance to convert and 70% chance to refuse to convert

The decision to accept the demand is further modified by:
The state’s current religion where orthodox, Coptic, Jewish and Zoroastrian are 80% less likely; Muslims are 70% less likely; Confucian and Shinto are 30% less likely, Protestant and Reformed are 10% and Pagan faiths are 50% more likely.
Religious Unity where higher degrees of religious unity make the state more likely and lower levels less likely
Stability where higher levels make the state more likely to accept and lower levels less likely
The presence of religious nationalism makes the target 40% less likely to accept
Government where republics are less willing to adopt religious nationalism and Celestial Empire and theocracies are more willing
The state is more likely to adopt if there are more than 3 neighbors of the same religion and at least equal power with whom it has bad relations
The state is more likely to adopt if it does not have any neighbor allies with its same religion
The state is less likely to adopt if it has a low degree of religious unity
The state is more likely to refuse if it has a neighbor ally of the same religion

Event where states decide to convert based on religious makeup

This is an AI only event that fires about every year. To fire the state must have at least one province of its primary culture (will not fire for say The Knights). The state must have a significantly non-state religion (number of provinces that have religion X when state religion is religion Y).

The mod calculates the ratio of the total amount of state (non-territory) core provinces that have the owner’s religion and culture to the total amount of state (non-territory) core provinces that have the owner’s culture.
The mod calculates the ratio of the total amount of state (non-territory) core provinces that have the owner’s religion to the total amount of state (non-territory) core provinces.
The mod calculates the ratio of the total amount of state (non-territory) core provinces that have the owner’s non-state religion to the total amount of state (non-territory) core provinces.

The AI will then pick an option to convert to a non-state religion or keep their original religion.

The AI Chance for the choice to convert to a particular non-state religion is primarily driven by the ratio of the total amount of state (non-territory) core provinces that have the owner’s non-state religion to the total amount of state (non-territory) core provinces. This is directly applied in increments of 10% so that a value .4 is a 40% chance etc.

The choice to convert to a particular non-state religion is further modified by:
The target’s current religion where orthodox, Coptic, Jewish and Zoroastrian are 80% less likely; Muslims are 70% less likely; Confucian and Shinto are 30% less likely, Protestant and Reformed are 10% and Pagan faiths are 50% more likely.
Control of applicable holy sites. If the non-state religion to be converted to is Catholic and the state controls Rome and it is Catholic then this increases the chance. Similarly if another Catholic state controls Rome and Rome is catholic then this increases the chances. The control of holy sites variables very by religion.
Stability where higher degrees of religious unity make the target more likely to and lower levels less likely
Domestic structure where Celestial Empires and theocracies are less likely and republic are more likely
The presence of religious nationalism makes the target 50% less likely to convert
If the two nations are from different religious groups then the target is 5% less likely to accept.
The ratio of the state’s primary culture that has its current state religion such that the higher percentage of the primary culture provinces that have the current state religion the less likely the state is to convert to a different religion
Some religion specific additional modifiers. Muslim and Christian group nations will not convert to pagan. Muslim nations are very unlikely to convert to Hindu

The choice to stay with the current religion is modified by:
A baseline of the ratio of the total amount of state (non-territory) core provinces that have the owner’s religion to the total amount of state (non-territory) core provinces directly applied so that if 40% of the provinces have the state religion then there is a 40% chance to choose the option and keep the state religion

This choice if further modified by:
Counter effects for the religious sites modifiers. If the state religion is catholic and the state controls Rome then it is more likely to choose to stay with a state religion as catholic.