I do this for my non-Tormach machine in the tormach_mill_base.ini file, depending on your machine you might have to pick the appropriate _specific.ini file instead. Your log file near the top will show which specific .ini files were used. Note that there is also an autogenerated .ini file, any edits to that get overwritten everytime you start PathPilot.The autogenerated file has a warning inside at the top as a reminder.
Look for the [AXIS_0] section, in there is MIN_LIMIT and MAX_LIMIT. You machine will still home to the limit switch, but Gcode will error out if you go beyond the limits.
You can also add HOME_OFFSET to back the axis off the limit switch farther.
Gerrit