Alexander Blade, known for opening the door to modding GTA IV on PC has recently released working files that will do just that once again for GTA V. While he has yet to release the SDK for other coders in the mod community, he is planning too and we will soon witness a modding renaissance in GTAV.
The ScriptHook & ASI Loader were required to load famous GTA IV script-mods, such as Simple Native Trainer, Iron Man IV, Left 4 Liberty & LCPDFR.
While Alexander has coded the Native Trainer to NOT work in GTA Online, in general, it is recommended to avoid using mods online as abuse can result in a ban.