changing the firmware on an e260r with ver 1

I have 2 Sansa’s … 1 is an E260 v1 (with the latest firmware) and the other is an E260r (Rhapsody) … I would like to change the firmware on the “r” unit to a Ver 1 .    Will this cause the unit to lock up or be made in-operable?

It could. I haven’t heard of anyone who has done it. But the ‘R’ (or Rhapsody) player is in fact a v1 model, just with slightly different hardware inside for the Rhapsody functions.