You would probably be pleasantly surprised with how easy handling modifications are in GTA:V.

The handling meta files are all XML now, in more or less plain English, and very well documented by the modding community.

I run an GTA:V multiplayer RPG server using FiveM[0] and the community around vehicle mods is really incredible. 3D modelers produce all kinds of real-world vehicles for GTA:V from Nissan GTR’s up to hyper-accurate law enforcement Dodge Chargers[1] with accurate Whelen lights, Setina bull bars, etc.

[0] https://fivem.net/ [1] https://redneckmods.com/product?id=3fbaf24e-7775-432e-87e1-f...