Ok, so there are chips and tuning boxes, how about

people adding a S/C or swapping the turbo to a larger one? Has it been done?

Look at the entire thread entitled "Special Projects" (Evil Beetle).

There, you will find the saga of Mickey, who after destroying his compressor on the high altitude mountain highways of Utah, needed to replace, and chose bigger!

Have fun!

(But with that exception, there are few cases of non-emergency turbo replacements. It's just too damned expensive!)