Acids usually do a good job of removing blue. Vinegar is a weak solution of acetic acid. The vinegar/H2O2 mixture is some times recommended for removing leading from a barrel, but many think it is a bit too aggressive for even this application. Unless you have been firing cast bullets through your M-N, an ammonia based bore cleaner would probably work better, or a session with J-B bore paste. Discretion is advised in either case.
As far as re-bluing goes, I recommend staying away from the cold blue. A hot salt blue requires a lot of equipment, dangerous chemicals, and dangerous temperatures, so I don't recommend it either. (Yes, I know lots of people do it at home, please be careful).
That leaves rust blue, (heat blue is a possibility for some gun parts, but not barrels of center fire rifles). Rust blue is easily accomplished at home, but is very labor intensive. Your M-N, if it is old enough, may be rust blued.