How to edit .MOS files?

Hi all, new here but enjoying the games nonetheless. I was thinking of making a couple minor tweaks to the UI but can't figure out how to convert the .MOS image files to .PNG in order to edit them. Photoshop won't open the .MOS files directly and neither will IrfanView. NI doesn't seem to have an option to export them to .PNG, and I get error messages when I try to view most .MOS files in NI anyway so I can't even see most of them to know which one's which. Any help would be appreciated. Thanks!