Tom,
You are correct about having to delete a pattern to put a new one in it's place. I know in 3.0a or in 3.1a you can just hit pattern edit first, then select the pattern of patterns you wish to delete and then push I believe it is F6 for delete and your patterns will become empty. This doesn't push the patterns left together, you just end up with empty locations. In 3.1a I think I remember that you can delete all patterns from the load screen but I don't remember, because I am not at my store right now, if you can delete only one selected pattern from this screen. I hope this helps answer your questions.
George Kaye
Kaye's Music Scene