Is is possible to have 3 different loops loaded and not allowing them to play at the same time?
Loop 1 is playing
Pressing loop 2, starts loop 2 and stops loop 1
Pressing loop 3, starts loop 3 and stops loop 2
Sorry about the delay @Craigzilla - no, not right now, at least not with Loopy HD on its own. You could use a third-party MIDI processor tool to send multiple messages to Loopy, each one sending play/stop messages to each track.
But Loopy Pro will do all this and much more, coming soon - see https://loopypro.com to be notified.