Summoning numbers work the same as damage rolls. That is, if you specify 1d6 of something, and then roll a 6, the game subtracts 1 and then adds another 1d6. If that second roll is also a 6, the same thing happens again.
This means that a ritual that summons ore than one of something can potentially summon any number, depending on the roll of the dice.
Another implication, which may or may not have been intended, is that a ritual that summons a small number of creatures is far more likely to exceed its 'normal' effect than one that is designed to summon a large number. This happens because if the dice being rolled has less sides, it is more likely to roll the highest value and thus trigger a second die roll.
I haven't done a thorough statistical analysis of this, and I won't, but it seems likely that there will be some 'edge cases' where increasing the die size by one would actually decrease the average number of creatures summoned (note that calculating the exact average number is impossible, since the number of dice rolled is potentially infinite - we can only approximate, by excluding outcomes that are so improbable as to be unlikely to occur even once in a very long period of play).

clearritspec does not completely clear a ritual; it only removes some attributes, while leaving others intact. Notably, it does not remove strings. To my knowledge, there is no way to remove or change a string from an existing ritual.

This topic may be of interest to you: What does clearritspec change?

In it, Xelos offers a workaround for a situation similar to yours.

Hope that helps!

Thanks to both of you for the explanation :) I figured the dice rolls worked the same as they do in Dominions 4, but since I couldn't find it specified in the manual I was starting to have doubts.

That is a decent workaround. Do you know what would happen if you make the new ritual have the same exact name as the old one set as no start? I'm gonna try that now.

EDIT: it seems that simply creating a new ritual with the same name does not replace the old one, but rather leaves both ritual as existing, so indeed, marking the old one as nostart is the best thing to do. However this means that one can make the new ritual have the same name for an unnoticeable replacement, since the player will still see the ritual with the same name and everything.

I discovered a new trick

rather than use clearritspec with its unknown useage or fiddle with nostart and hope for the best simply take the existing ritual which needs changes to AP or summoning string to lev 9 and redefine the ritual at a useable lower level, that is lev 1, 2, or 3

levels 4 to 9 rituals are all undefined as others have posted. avoid using level 4 for hiding spells since in some cases in crashed the game upon startup. I have had no problems using level 9

selectritual "Create Wood Golem"
level 9 # not possible to invoke

newritual "Create Wood Golem"
ritpow 11 # enchantment, modifies last new or selected ritual
level 2
< proceed to start over from scratch with new summoning and new AP cost, etc. >

this technique's only drawback is if the ritual to be changed is unknown (but version 4.24 rituals from CoE 4 exe were just posted) or has commands that are hard coded (noted in 4.24 rituals just posted)