I've done some "cosmetic surgery" on fish in the past. Simply from my experience, I catch the fish, place in large ziplock bag (protects Slimecoat), push fish to bottom of bag, cut small opening in bag appropriate for surgical site, place fish on flat surface and hold fish down firmly while performing the surgery. Then simply place fish back into tank from bag. I've done this cichlids, datnoids, Arowanas, etc. Sometimes, I don't even do any cutting, simply "rough up" some fins to encourage regrowth that I'm certain would not regrow on its own. I've used sedatives in the past too, can be a bit scary the first time. I do work in the medical field, around procedures all the time.