Just my comments.

                I generally just make a new copy of the code, give the
old version a rev number (mycode_0.asm), and just cut out the code I
don't want, assemble, test, debug.  If the new code works, great.  If it
didn't go back to the last good version and continue.  Also, comments at
the top for each new code revision helps too.

                We all program differently.  This is just how I do it.
Applies to C, assembly, and now my verilog