I know this is likely a kind of a dumb question, but can anyone put my mind at rest if you know exactly.   I cant alter my details entered for bitcoin address to use from mycelium that I've previously used and received funds on, so I need to keep using that address as its registered a few places.
  However mycelium itself no longer displays that address, its showing my address to give out as something different.   Its not the first time Ive seen this system and I know maybe some security is increased by them altering my address for me, but I do still have the ability to receive on my old address from October right?   Just wanted to check its not going to be a problem.

I will of course sift this thread for similar queries / answers.   I presume its fine just its not exactly smart to presume and not double check