Can you explain what you are trying to do with M10 and M11?
In your post you put this, but it does not make sense what you are trying to do with it.
Pay attention to the next sentence!
Just change the plasma profile so that the interpreter will trigger the M10Q255 only if the speed is over 90% of the last set !!!
Are you using the pwm signal for something?
You can use one of the other mcodes m208 etc (I am on a phone and forget the numbers) to trigger an output when the actual feedrate goes below the set feedrate (90% or whatever you set)
Just wire this output pin up to inhibit thc.