Not that I am aware of in open class racing at any "meaningful" events (I know meaningful is somewhat subjective). It has been done at F16 only events (example: nasty weather on Saturday and good weather on Sunday).

Robi - you mean on an event-by-event basis, right? I whole-heartedly agree that once entered in an event you should sail in that configuration for the duration of the event. I do think I should be able to sail 1-up at one event and 2-up at another event, though.