BL1,
Although I agree with Willi that it can be done, I would still advise against it.
Over the years I have had three different Mystery wrasses, mixed with Possum Wrasses, Leopard Wrasses, Fairy Wrasses, and Pink Streaked wrasses. In all three cases even though the Mystery Wrasse was the last in, and I got them small eventually there was some aggression, and as it got larger, the aggression intensified. It never got to the point of that they could not be together at all (had them in both a 75 and ten a 150 gallon) but it definetly affected the behavior of the fish he was bothering. In my case it was usually the BSLW, Pepp Hogfish, fairy wrassses.
If you do do it the smaller wrasses that spend a lot of time in and out of the rock work seemed mostly unaffected. Although the mystery wrassses are beautiful fish, my experience is that they become pigs for food (grow faster than almost any fish i have ever had) and get meaner over time.