Why not just cosmetics for platinum medal?
MT: Welding goggles with a glow in the dark, NVG-green to the eyes. Doesn’t help them see in the dark. Just makes their little eyes glow green in the dark - like, as much light as a cigarette/cigar gives off.
MP: Judge Dredd helmet - same stats as a standard MP hat/helmet, just a different look. We already massively reference Star Trek with literally EVERY medicine so why not another beloved Sci-Fi? This one is even fittingly dystopian.
Doc/CMO: A big googly-eyed headpiece with a bunch of different lenses on it, like Ichabod Crane’s weird magnification device in the Burton Sleepy Hollow. Or maybe the creepy doctor turtleneck from TimeSplitters.
Command Staff: Obviously, privateer gear. Tricorne. Parrot that fits in the off-ear slot but shows up on your character’s shoulder. Big pirate-y frock coat. Powdered wig.
RFN: Squad specific half-cape that fits on your mask slot, goes down maybe to mid-back/waist. A battle skirt ala Clone Commander style or some sort of half-cape over one shoulder would be cool too. OR… SQUAD SPECIFIC BERETS THAT ARE ACTUALLY THE SQUAD COLOR AND NOT THIS SINGLE PIXEL DOT OF COLOR ON A GREY HAT.
Engi: Welder’s mask with hotrod flames or some painted on dragon/lion face. Or maybe their armor has black/yellow hazard stripes.
Medic: Plague doctor’s mask. Nuff said. A white cape would also be cool but it would make you extremely obvious to xenos. Guess the mask would too, but…
CT: Some sort of mini-exosuit harness. Obviously no stats, just a little power armor kinda rig they can wear on their armor slot or something to make it look like they’ve got help in tirelessly moving hundreds of boxes of ammo, nades, building materials, etc.
Then you could just pick which cosmetic you want, if at all, somewhere near and in a similar fashion to how you pick your custom loadout. I’d sprite all these no problem if anything like it got off the ground.