I've actually been looking into this myself recently; it's funny you should make a post here around this same time. Colosseum is easily my favorite game, and I've been searching for a way to play though it with a twist.
As far as I can tell, Shadowth117 is correct; there are no randomizers in existence for Colo/XD. What I have been able to find however is a
So the groundwork for editing individual Pokemon is there, but implementation of doing so to every pokemon of every trainer with the game randomly is a large step in another direction. Although it would certainly be easier then a main-series game, as Colo has much less encounters and trainers then the standard game, from what I've read, one cannot simply apply something like the Universal Pokemon Randomizer to these games, as Genius Sonority apparently created the game's data slightly differently then Game Freak.Again, a randomizer is not impossible, but rather the tools and information known for the Colo/XD series have not been implemented towards that end goal. I personally would be more then happy to lead the development of said randomizer, but unfortunately I don't yet know all the technical know-how for the stuff behind the scenes. If anyone more knowledgeable would be willing to provide the already established data for the series and get me started in the right direction, I would be willing to pursue the creation of a randomizer.