Hello,
I also have accessory nerve damage from a severed nerve during a lymph node biopsy. After months of nerve testing and physical therapy, I was able to have a reattachment surgery that does not appear to be successful. Although I had very intense pain during the first year, it has lessoned over time. I have heard of the Eden Lange procedure, but to be honest, my pain would have to greatly intensify for me to consider it. I have already lost mobility and to some extent health. I am fortunate to have access to weekly physical therapy that has greatly reduced the pain and has increased my range of motion.
Hope you find an answer to your question and find peace with whatever you decide.