There should be an option to Delay a mission, as well as Scrub it, in the VAB/VIB and maybe other places. From time to time I have a mission scheduled to launch, but the hardware isn't quite ready. It would be much more convenient to tell the game to delay it a turn rather than scrub it and reschedule the whole thing.

There's a newscast which does exactly this, so it shouldn't be difficult to implement such a feature.