Client has a Prostar DCS Compact with three lines. I cross-connected a 4th line, but cannot figure out which MMC(s) to use to allow sets to display/access the new line. Sets are 10 button.

Button programing. DS= direct station, DT= direct trunk

So it's done per set, not per system?

You can do it system wide too. Its the mmc above the single station programming.