If you find yourself undoing automatic script actions by hand, something is really wrong already. As such, you are asking for a feature that will help you resolve the symptoms of your problem, not the problem itself. Instead, if you do not want those "no update" lines in your log files, you should modify the youtube script not to log them. This is pretty easy once you know what to do, and there are other section of this forum where people will be happy to help you out. I think you'll agree that you, too, will be happier if you don't have to edit your log files at all anymore, right?
As for your actual request: log files are supposed to be append-only by nature, so I also disagree that mIRC should have a facility to edit them. But as usual, the ultimate decision is with Khaled, so please do not take offense to people suggesting it is not a great idea. It is just a natural part of the discussion. If Khaled likes your idea, he will add it anyway.
