In the main dimension, at SF airport there is a mod shop on the west side, near the entrance. I'm sure this can be used in apartment dimension instead of relocating another. Thereafter I suppose you can test your vehicle on the airport strip so I don't see a need to have many modshops around the map, just 1. (Just my opinion)I strongly support this POSITIVE
I think this would be great and useful for quite a few people but who are selling engine parts? If the player can use the engine part safely then the people selling the engine part won't make a profit, I know although the engine part can do a lot of other things too but opinion Although it was very useful and I liked this too but in my opinion it was unnecessary as this would make the engine part no longer a bulk purchased item, so I won't support this for now but I will continue to follow this topic and read more comments and maybe I will change my mind too.
Engine parts are very expensive to buy for testing a vehicle. I like your idea because it will help players to be specific with which car will they tuned, it will also improve activities that can be done inside an apartment like racing, drifting, RP and a lot. This suggestion is very useful to new players too. I am supporting you
I also suggest that when you put a tune on a specific vehicle, even if you re-spawn it with /createveh command it will have the same tune being saved.