>> Is there a way to edit a title of a song performed so it gets changed on every setlist it appears on?

Yes. Ask a Moderator and we can take care of it.

>> if a band do a medley in concert, and it's all cover songs, how do you do it so that the songs are linked but also have each individual artists at the end of each track?

I'm not quite sure what you're asking, but I don't think it's possible. The closest would be to add the artists with the @Info tag.

>> eg: if the Status Quo did a medley of "Caroline"/"Down Down"/"in the Army Now".... the former is a cover track, but the other two arn't.

If "Down Down" and "in the Army Now" are on the same album, we can assign the medley to that album. If not, then it won't be assigned to an album.

>> if, say, Paul McCartney decided to do a medley of songs in concert... "Crocodile Rock" by Elton John, "Part of Me" by Katy Perry and then "Cum on Feel the Noize" by Slade (a strange set, i know! lol.) how would you list it on the Setlist website?

Crocodile Rock / Part of Me / Cum on Feel the Noize

>> Cos if i put them three as a medley, it won't allow me to say who each original artist was.

Right, this is currently not supported.