I have, but the biggest problem (as always) is not the garage locations but the pit spots (especially with AI). There is plenty of room behind the pit building and it should be easy to create 50 garage locations there, but all cars have to do the pit stops in the pitlane and most leagues want to have individual pit spots for each car. There is some space left and with some tweaking it should be possible to squeeze maybe 50 pit spots in the pitlane. More than that and the AI creates mayhem.

If you start a session with more cars than garage locations, rfactor creates new temporary locations in front of the existing ones. I've tried that (with 103 AI) and it works good, only problem is that the cars in the second row are blocked until the cars in front leave the pit.