Open up the ck3 launcher. All installed mods. Upload mod. Create new mod. Any name, whatever current version is, directory is the name of the folder in your mod files so give it the same name as the mod.
Go to the file of this mod. This is in documents -> paradox -> Crusader Kings III -> mod. The mod you made in the launcher is here already.
Go into that. Make a folder called common. Make a folder in that folder called holdings.
In that, make a file with notepad and save it there. The later in the alphabet its name (like if it starts with a Z) the more it'll override the holding files of other mods and vanilla... which is what you want.
Program Files -> Steam -> Steamapps -> Workshop -> Content -> 1158310 -> The ids of the mods you wanna make a compatch for.
The id of a mod is the number in its link on the workshop. For example this mod's id is 2778057631, which you'll see in its link.
In the folders with those ids, open the holdings files, which are in common -> holdings. You'll see the format. You want your mod's holding file to look like them, but with all the same building ids between the brackets of the holdings.
You can also use this to remove certain buildings from your playthroughs. You might also be able to make certain buildings accessible in unusual holdings, although this is limited as some buildings have it set within the code for the buildings themselves that a certain level of a certain holding type is reached within the holding, and upgrading of such buildings would be especially limited.