How to stop the "topic" line from getting repeated in every reply post???

[Arantor]

Using full edit on the subject works on the OP (and of course adds the changed subject to all other posts in the thread)

Not in 2.0, it doesn't. It only touches the original, all the replies that currently exist will use their original title, while all new replies use the new title. This is why it's a lot more complicated to fix than just switch'n'bait on the display.

[Antechinus]

Hmm, will have to check it again. Anyway, although that would matter for trunk I honestly am not too fussed about it for my own use, since hardly anyone ever gives a rat's about individual post titles in practice. Basically, if you just want the display cleaned up for less clutter, and aren't too fussed on the trivia, it's pretty easy to do.