Hi ! I'm sorry, I don't have the answer BUT I would like to know that too ! I'm trying to create a similar mod and It's super hard without changing this formula ...
Dismemberment works in a very weird way at the moment and it's just not balanced at all ! I mean, why does people will shoot the legs if you deal 3 times more damage to the head AND you have the same chance (or maybe more if this is linked to damage dealt) to dismember ?! It needs to be changed !
I've done some researches and I've found just one clue to modify or just understand this formula ... You MAYBE have to search in the file nammed "Assembly-CSharp.dll" (can be found in : steam/steammaps/common/7DaysToDie/7DaysToDie_Data/Managed)
Link talking about this:
Unfortunately, I don't have the skills to understand this type of content and I guess you don't too if you're new to modding ^^'
What is your goal exactly ? Do you want to change dismember chances in function of hit locations ? In function of the type of enemy (Feral, Radiated ...) ? In function of the weapon used ? Because you can do some basic things without changing the formula ^^
PS: I hope it was understandable, sorry I don't speak english very well ^^'