If the LE Only rifle was legally obtained by the original dealer and end-user, and not a rifle purchased for the purpose of parting out or any other illegal purpose, then its status as a post-ban, semiautomatic assault weapon (SAW) ends when it is reduced to a stripped lower or when the number of "evil" features is reduced to only one. Since it is no longer a SAW as defined in Title 18, USC 921(a)(30), it is no longer regulated under Title 18, USC 922 (v)(1).
There is no law currently on the books making it illegal for a non-LEO or authorized agency to possess a rifle marked for government or law enforcement use only if the weapon is not in SAW configuration as defined in Title 18, USC 921(a)(30). The only problem a non-LEO owner of such a weapon would be how to explain possession to an officer who doesn't know the law.
It will be interesting to see BATF's answer since they apparently haven't promulgated any regulations essentially saying "Once a LEO Lower, Always a LEO Lower," as they have with machineguns. We'll see...