I have seen several work arounds and heard of others.
1. If you see this is a box on a bar hanger, remove the box, attach a second handy box to one side with a chase nipple or offset nipple. Move the NM to the new box. Make a splice to some NM-b or THHN in the second box and put a cover on it. Then you can shove the whole cludge up past the bar and reattach it. This is still "accessible" since you installed it without disturbing the finish.
2. Some kind of shrink tubing to bring the NM up to 90c standards YMMV on this with the AHJ.
3. Knock the old "nail on box" out, splice the NM to NM-b with an Enerflex device and install an old work (bar hanger) box. Or see #1 once the box is gone.
