Here are some last ditch options IMO. You are in the hole already so this is what I would try. Leave the yellow in the QT for now. In the mean time rearrange the tank and let the naso settle for a few days. What I have also done before is used those guppy breeding tanks made of clear plastic to seperate quarelling species, but this was with smaller fish, and done at introduction. That probably wouldn't help seeing as this is a problem that developed. Regarding territorialism, there are basically two types, the ones that get better and the ones that get worse. The only ones that get better are when fish are introduced and the aggression dies down. Anyway, try what I said above. When you add the yellow back see what happens. My guess is that the aggresion will be go away only to come back when the yellow gets comfy again. Be careful though, all that moving of tangs is stressful and even a novice is familiar with the disease magnets called tangs.
Oh and by the way, the trimming of the surgeon I have never heard of and wouldn't try myself. Even without the surgeon, the tang would probably continue tail waiving until it was stressed out. Yellow tangs are little #^%$&&es and should be saved for larger tanks. Maybe they get mad at all the snooty more expensive tangs?
