Ooops. I mistook your intent - that you wanted just the drive space.

If you already have music on the reused drive, leave it alone. The only trouble will be to resyncronize the FIDS. I am not sure of the best way to do this off hand...

Edit: Basically, the problem would be that if the reused drive was primary, there would be a root playlist on both players, and FID numbers that would appear on both physical drives. You would have to renumber the FIDs on the reused drive and link them into your playlists somehow. Not sure of the best way to do that.