Is it possible to programmatically alter a ARMv7-compiled binary to replace all the new opcodes and instructions with ARMv6 compatible ones?
I don't really care that much about performance at this point, I just want to use some ARMv7 only binaries on an ARMv6 (with vfp, if that matters).
vfp will matter if using instructions not supported on ARMv6 unless those are the ones you are replacing.
If we are talking just arm instructions not armv6 it is probably a short list. It is probably reducing the number of instructions though so you would have to modify the code such that the armv7 instruction causes a branch somewhere, that somewhere is the replacment code using armv6 or older instructions, then branch back. not branch and link, unconditional branch or ldr pc,something, etc. if you are talking about thumb2 stuff that may still be possible but probably more work, some things you might not be able to do.
short answer: Yes in general this kind of thing can be done.