I have a Rock River Arms M4.  The barrel has a fake birdcage flash hider on the end of it (like all the RRA M4geries do).  Those who have the gun know that this is 100% purely for cosmetic reasons and doesn't affect the legality of the RRA M4 in any way since it doesn't add to the length - it is almost like a "sleeve" that goes on over the end of the barrel.  My question is:  Is it permanently attached, or is there some way to remove it?

It's pressed-on.  It can be removed, but it isn't easy.
Sluggo

It can be removed, but the muzzle has been turned down too far to thread it for a regular type muzzle device.