I am digusted of the thought of going into the UNIX land and learnign a new inconsistent and incomplete regexy shell syntax. So, if anyone adds a Makefile that:
Generates mbf(r|l).min.bf from the respective source file by removing all the non-BF characters.
Generates repl.bf from mbfr.min.bf by adding a required set of strings before/after the the code from mbfr.
Generates repl.min.bf stripping all the non-BF from repl.bf.
Nothing especially complicated, but the best I've arrived at was:
cat mbfr.bf | sed 's/[^-+<>\[]//g'
which does not remove newlines (unsurprising given sed being line-based) and removes closing brackets (as the character set syntax seems to not have a syntax (at least the one I know of) to include literal ] character.)