Sadly it seems curses and blesses from a mod have a extremely rare chance of happening. Ive only had it happen once and that was from tipping over a statue.. after about 30something resets (from when i was testing it, altho at this point I am not sure what the conditions were of this happening, such as it being based on a specific type of god or anything). I havnt been playing DF much since the testing back in december since ive been busy with other things.
This is because of the way vanilla curse interactions work. Each type of werebeast or vampire is
its own interaction, and the game picks one at random AFAIK - in other words, if you have a world with 40 werebeast types and 40 vampire types, you will have a roughly 50/50 split between werebeasts and vampires. Someone getting were-cursed will take one of 40 possible forms, and multiple forms may end up with the same animal but different weaknesses and appearances. I believe all vampires are more or less the same right now so the only difference is frequency of occurrence.
Thanks to how this works, modded interactions become extremely rare unless you have a way to work around it. Potential workarounds include DFHackery or manually duplicating each type of curse interaction a number of times based on how many types of weres/vampires you want your end users to use. Types of each of those can be directly controlled in advanced worldgen; don't know the default values (for the normal worldgen screen etc.) off the top of my head.
If you go the duplication route, you'd essentially just be doing SHRYLING_1, SHRYLING_2, SHRYLING_3, ... (as an example) with no changes to the actual raws between each one: you're manually increasing the weight by having a bunch of copies of what amounts to the same thing.
Yeah I know this is a necro but whatever, at least I helped explain what's going on, right?