Create own Add-In to update folder card variables

Hey Guys. I am new to this forum and I am standig in front ob a (in my opinion) big problem. I am currently working on a system to generate a certain part of our companies drawing number out of our folder cards and then just add a partnumber to the part itself to generate automatically our draw. nr. Therefor I made a template to generate automatically our normal folder structure including a completely feeded folder card. The Problem is, that I have one variable that consists of 3 other variables but this variable is only updated when I change one of the 3 it consists of. My support told me that it is not possible to update this variable with a dispatch. So I want to create an Add-In which updates every variable on a folder card. The only problem is that I have absolutely no idea how to make my own add in. Can someone help me? Thank you very much in advance and I hope my english isnt that bad that the problem isnt clear.