I have done it with a Potter's, and added a multicolor to a tank that had 2 other dwarfs.
First, I would get an acclimation box -- I left my multicolor in there for a week. It allowed all the fishes to get used to each other, and I was able to get the multicolored used to the food I use and eating. (( If there is some chasing/hiding you want it to have some fat on it )).
Second, have a back up plan -- sometimes it just doesn't work. It can be a PITA to remove an angel from a reef.
I would try to get a smaller one (( by a decent margin )) then the existing one.
This is the acclimation box that I had mine in; it is 12 inches long,