In the past, Rockstar has actually been supportive of GTA modders. As pointed out by GTA Online News, you can find blog posts on Rockstar’s official website sharing video links to popular GTA mods that use OpenIV. And in an May 2015 Q&A on Rockstar’s website, they said they “have always appreciated the creative efforts of the PC modding community and we still fondly remember the awesome zombie invasion mod and original GTA map mod for GTAIV PC among many other classics.”