Medicare Insurance Issues?

Anyone have Medicare for primary? Do they allow revisions? 

I have Medicare primary and a med supp.  I had a revision from lap band to RNY last July and Medicare paid for it with no problem.  I had to complete the NUT class and pschy evaluation prior and then a date was scheduled. It will be one year this coming Wednesday since I had my surgery and I am so glad I had it done.  Even though I was 70 when I had it done, I think I have added years to my life by getting off as much weight as I have.