When replacing a turbo sometimes the old studs are perfectly happy remaining in the turbo. Some of the time you can get them out using the double-nutting method but a lot of the time they just shear off. If you are going thru all this work, you might as well just replace them with new ones for a hassle free install.
Warranty Disclaimer:Subaru of America will only warranty parts installed on a car that has a matching VIN to that part.