I have actually used that technique years ago to re barrel a Python and it worked well.
One concern for me is "Will the bbl. be tight enough after I back it out that 12,000th of an inch."
Actually, with the Python, I clamped the frame in a big vise, between two pieces of soft pine which were padded with towel material, and used a well padded wrench to remove the bbl. and replace with the shorter bbl.
Worked well with no problems.