How to cut bx cable without a hacksaw

With a BX cable cutter of course...

Here is one I have... there are other brands and manufacturers of course.

Klein Tools 53725 BX and Armored Cable Cutter

If you don't have a hacksaw, I doubt you have a armored cable cutter.

You can snap the armor where needed and use a pair of diagonal wire cutters to cut the metal sheathing, once this is done, you need to rewind the sheathing back into place being sure to snip any sharp edges where the sheathing was cut.

Then install the "redhead", AKA antishort bushing.

Easier to show than put into words.