Is it possible to play just part of a pattern while editing?

I believe not. But I’d also find it very useful.

Maybe you can turn this into a wish? There’s a similar wish for the Tracker.

Edit: Oh, and for related discussions, I think this wish about rendering a selection into a sample is relevant. It may even be something that would make sense to implement at the same time, as both ideas revolve around working with a selection only.