When adding the MC Etcher toolpath, I get an error " “RPM” must be between 1 and 100000" if any changes such as Stepover are made. RPM is supposed to be 0. This also occurs if editing the tool for example switch from a 120d to 90d MC Etcher or vice-versa.
I know I can go into the gcode file and remove the M3 command to keep the spindle from turning on but shouldn’t Carbide Create handle this natively or is it PEBCAC?
I just turn off the spindle on the machine itself and disregard the programed RPM. That way there’s no chance of me messing up. 
But you’re right in that 0 RPM could be specific to spring loaded etching tools. I don’t know the programming end of software makes that difficult though.
I took a chance and set the McEtcher rpm settings to 1 and ran it. The VFD didn’t turn on.
Note that if one uses the pendant/button to disable the VFD (or just unplugs it), then there is zero chance of it coming on.