iTunes Match and previous iTunes purchases

In a way yes it is possible. When you run match it'll probably pick up most if not all of your purchases. It did for me with the exception of a couple of tracks (some bought on iTunes stores from other countries). Once you have those purchased tracks matched, what you want to do is delete the purchased ones and download them from the matched copies. That'll effectively re-assign the license for the files to the iCloud ID. (you can check this by getting into from the track in the summary tab)

Now, concerning the purchased music that wasn't matched. What you will want to do is strip off the license to your old account. So convert the remainder of the songs to AAC files, 256kb (make the settings as the iTunes store would do it). Then run match, again if it doesn't pickup what's left, it'll at least upload the copy without the license to your old apple ID and assign it to the iCloud ID.

In effect what this accomplishes is it transfers all your music from one ID to another.