The problem is that when you need to rebuild your game UBT cleans the engine and editor along and thus rebuilds everything. If you are forced to rebuild your game code you’d go to manually delete the Binaries and the Intermediate under your games project directory, and then recreate the project files. I think you dont have to close VS for that, just reload the solution when the project files are fully regenerated. Then the games object and binary files are quite clean now, and you can safely Build them instead of rebuild everything.
I havent found any better way and if someone knows, please share 