Tormach has Purposly "Crippled" the Mach3 Screen that it sends to keep users from doing custom stuff, above and beyond what the OEM is willing to accept Liability from.
So, If you want to do what you want, then to keep your warrenty, contact Tormach and have them "Add" the inputs you need and perhaps modify the screen to your needs. I can't say that I blame then one single bit for the way they have done thier release model.
BUT, having said that, if YOU are willing to sign a Liablitly release for them (you can contact them to get one). Then you could just download a copy of Machs Screen 3, or Screen 4, to do your screen changes, AND you would also need to do a "Install" of machs latest Dev release, to "restore" the crippled screen back to mach standard.
In mach Standard install, and screens, it is a Non-Issue to do what you want. Again, though, I highly recommend you have Tormach do the changes you want, or sign a liablity release and do it yourself.
scott
Commercial Mach3: Screens, Wizards, Plugins, Brains,PLCs, Macros, ATC's, machine design/build, retrofit, EMC2, Prototyping. http://sites.google.com/site/volunteerfablab/