Swapping between ModBus or Step/Dir for spindle between normal and tapping?

I have a spindle servo that takes Modbus commands great (I have that worked out).. However, for rigid tapping I have been warned ModBus may not be a timely enough method.. The Spindle also takes step & direction great (however, at 4096 pulses/rotation and max RPM of 10k I can't run my spindle in step/direction normally as the pulses would be crazy small...

How might I configure/code things (or pointers to docs on this) where I can have essentially two methods for spindle control and flip between them based on if it's normally commanded speed or a rigid tapping operation where I want the servo and encoder to work with the z axis to well, do rigid tapping..

Thanks in advance.

Hurm... I see what you did there.. so a few "interesting" tweaks to the post processor, and documentation reminding myself what I did for after I have slept a few nights..

No way to do that "switching' between spindles by customizing the S command? like if S < 1000 use $1 if S > 1000 use $0 as a bit of a custom macro?

So its not something that is a command I could muck with like a macro then.. roger.. yah would not want to fork to solve this for sure..