This may depend on the DIY organiser, but with my organiser the brevet is not used until you submit the gpx file of the ride so no, it shouldn't do any harm as such. That said, if you do end up with a duplicate entry somehow, it would be helpful / polite to say 'DNS' (did not start) to one of them so that it can be properly flagged on the AUK systems. Chances are it just didn't submit first time for some reason though.