Well, we've had a few people rejoin after they'd left (having completed their contracts) and rumour has it that AJX has asked certain individuals if they'd like to come back. I also heard tell that some people who had not been successful were re-invited to apply after 6 months or so. Maybe they only just missed the grade, I really don't know.
The main point, surely, is what is it going to cost to have another go? A bit of internet access or a phone call and you'll get a pretty good idea. I think I would be tempted to use CREW if you previously used PARC and vice versa and, unless specifically asked, I don't think I'd make a show of having previously applied.
They are still very keen to recruit new FOs but Capts need to have a JCAB ATPL (and preferably the 767 type rating but not absolutely required), so slap in an application if that suits your wants.