Rockstar Games has released a statement on Grand Theft Auto game modding on its official support website. The statement was published earlier today.
In the statement the studio states that after discussion, "Take-Two has agreed that it generally will not take legal action against third-party projects involving Rockstar’s PC games that are single-player, non-commercial, and respect the intellectual property rights of third parties."
The statement further notes that tools, files, libraries, functions or other modifications affecting multiplayer or online services are not allowed. The use or importation of other game data in third party projects is also prohibited.