I'm so glad you haven't had any surgery yet!
Let me ask, if it isn't too intrusive, your "barnacle," have you had it looked at by your rheumatologist? I'm assuming, possibly incorrectly, that you've seen one since you got the polymyalgia diagnosis. The reason I ask is because my whole medical journey began with a simple swollen index finger and it was thought that I had carpal tunnel syndrome. I went ahead with the testing and surgery (after quite a bit of physical therapy and exercising) and woke up in recovery with my surgeon standing over me saying that there was way too much inflammation in there for carpal tunnel, and did anyone in my family have Rheumatoid Arthritis?
That began a very long quest to find out exactly what I had going on - because when you test negative for the easy things, like RA, lupus, etc., there are dozens of other auto-immunes that are not so easily recognizable and diagnosed, but once identified are just as treatable as all the others. That's the good news! I really wanted to let you know that these pesky auto- immune are a true pain in the patootie, but they are very manageable once you are correctly diagnosed.
Also, if you do wind up having the rotator cuff surgery, I really think that the one thing that kept me from a second frozen shoulder was that on my right shoulder, on my athletic trainer's recommendation, (he is actually the best person on my medical team right now as far as helping with practical day to day advice!) my husband got a therapy chair brought to our house on the day of my surgery, which was outpatient, so that when I got home, I began to do just a few repeats of the exercises that I would be repeating on the following days and weeks. I believe that by starting the therapy that early, I didn't begin to build up the scar tissue that auto-immune patients with our famous white cell proliferation are known for, thus preventing the frozen shoulder. Maybe I was just lucky with it, but every patient that my surgeon and trainer have tried this with have not had to have a second surgery.
In any case, I didn't mean to write a book! Let me know how you are doing and if you have any questions.