I reschedule stuff all the time, it's not a huge deal, you just copy a few items from one list into another, it takes a few seconds usually. And actually, I find I like it this way because if I hit a point where I realize I'm rescheduling too much stuff too often it tells me that I need to either follow through more often or not be so optimistic in scheduling things so much.

Committing to do a thing in a given time period should be kind of a big deal. If you don't need to commit to a thing in a specific time, then just leave it in a more general master list (e.g. monthly, or generic) and commit to it when you have the time.