Ignoramus30138 fired this volley in
:

If you want to, then you can rig a switch that is activated by the
back-gear lever, and reverses the motor command to the VFD. then, M03
will always provide the proper spindle rotation no matter what gear you
are in. One of these DAYS...... I'll do that myself, too.

Yes, this is actually a good idea.

One DPDT relay will do it, Ig. Don't make it too complicated.

LLoyd