Not sure if this a bug or just a preview of things to come... I have an Omega Force Armor MK XII and a MACO Armor MK XII, but not the rest of the sets, so I do not have the costumes themselves. On Holodeck, they look like other armor when activated for visuals. But, on Tribble, they show up as the full costumes. Even their icons in my tray are different.
If you have the armor (and only the armor) you can display the MACO/Omega/KHG 'default' visuals on yourself or your Boffs the way you can any other type of armor (using the enable/disable visuals toggle).
There's no customization available unless you've unlocked the full set and the costumes projects from the rep system (separate projects).
Also, there's no customization of any kind for your Boffs which is really, really lame.