By interactable you mean "click X, Y happens"?
Removing source point cost is easy and I was actually typing it out but I realized you might need to do some reading first. Here's where you can start:
General documentation on skill creation (and by extension editing)
https://docs.larian.game/Skill_creation
Here's a tutorial about creating skills (aaaand editing) that goes further into detail:
https://docs.larian.game/Part_1:_creating_a_new_skill
The second link also includes some info about using the resource manager, stat editor... etc etc, things you need to know when modding the game using the divinity engine.
Hope this helps! :D
