[bazdan902]

I've made overlays before but for the life of me cannot recall how.

Nevertheless Looking at calterm though it looks like you can save screenfiles in XML format. I would set up your screenfile for the overlay inside a cal, in other words open up your calibration, open all parameters you wish to change, make your changes. Save screen file as XML. Open an unmodified calibration and use the screen file you just created in the overlay tool, run a compare afterwards to ensure it made the changes you wanted