I don't think a key change is, in itself, a big deal either. It might be a problem if you'd picked up a particular version on the net, say, learned it in that key (thinking it to be correct) and then got to a session to find everyone else was playing it in another key altogether! Not everyone can instantly transpose on the same instrument, particularly if it's a "fixed" one like a 1-row melodeon.

As for sessions, it would be unhelpful to lead off on a tune in a particular key knowing that the convention in that area, or pub or session or whatever, usually took it in a different key. Anyway, the lesson for me is to get a better grasp of my instruments so that I'm able to switch from key to key as need arises. As I'm a string player, that's not an insurmountable difficulty - just more practice!

Still, it's interesting to know that even modern, composed tunes can undergo sea changes, even in these modern times.