I keep all the old parts I swap out for gee-whiz parts. Still have my stock turn signals, exhaust can, etc. Anything not completely worn out like old chains or tires. I also prefer mods that aren't permanant. So I screwed down my indiglo gauge faces without using the adhesive. I got flushmounts that didn't require any cutting, same as I did with my frame sliders.
The only thing ireversable I did was hack off the fender and swap grips. Other than that, I can return my bike to stock. Oh yeah, and I had to can my rear sprocket from wear.