I prefer the way world of warcraft did it.

I had an original amani war bear mount which was exclusively available between patches 2.3 and 3.0 if you completed a very hard timed dungeon available once per 3 days (1 mount per completed run and there were ten people per run, so also limited by that). Some years later after people complained about not being able to get it anymore blizzard added the amani battle bear mount which is visually the same but a recolor. That way you still get the cool mount but the og earners still feel special.