Probe.dat file: copy a .3x10 tip, paste to make a duplicate.
Rename the item to the .2x10 and correct the sphere size from .3 to .2
You will need admin permissions to do this.
I also recommend making a backup copy of your original probe.dat file before making any modifications.
For real though, you're probably gonna wanna play with touch speeds depending on your tolerance zone... that little feller is gonna flex pretty bad, I'd imagine...
I've not looked for a very long time but is the usrprobe.dat file no longer used? This used to be the way to add a new probe without modifying the probe.dat which may be replaced with future version updates?