I use to know the DMS command for assigning SOI to the different MFD's and HUD but have forgotten that method. I've always pushed the OSB next to the lit up function on the MFD you want to have as SOI. In other words, if you want the right MFD as SOI and you have the Maverick page up on it, just push the OSB at the bottom of that MFD that has MAV lit up. Two presses of any button at the bottom of the MFD will make that MFD SOI in whatever mode you pressed at the bottom of the MFD.
Now that I've made this as clear as mud. I hope I didn't befuddle the whole thing up for you.
Edit: I just checked the manual and on the A-10C use the Coolie Hat to assign SOI. Up, long press makes HUD SOI. Left, Long makes the Left MFD SOI, and a Right, Long press makes the Right MFD SOI.