Although I haven't had dialation surgery and don't know much about it, I want to give my opinion about stretching body parts.
I've read about the stretching of the urethra (the tube from the outside of the body to the bladder). In years past, urologists performed it regularly for some types of bladder pain. They now regard it as damaging and antiquated. It was damaging because it was an uncontrolled stretch. I think they mean that there was too much stretch in some places and not as much in others. In some patients, the results were disastrous. This makes me shiver and cringe, much the same reaction I feel when I hear of an anal sphincter stretch. It seems it would follow the same principle.
If I were you, I would explore that option very carefully and with much doubt before submitting to it.