I've never tried this with a "plume" before but I guess you could try and dig into the, "colour atlas" and make a plume with a double color mesh adapt a green color channel so when "in-game" it would pick up the same color as another uniform part like the collar & cuffs, but I don't know if it will work i've never tried it. It also depends what kind of plume "mesh" you are messing with because from what I understand there are one colored meshed plumes and multicolored 2-3 colored plumes. and as for making a plume centered on a hat I believe you need to know how to edit a unit part in a 3-d graphics software which I know nothing about. Uncle "Steph" will see this and will hopefully come around shortly and answer this lol he always does. As for that shape of plume you are looking for,I have not seen in this game.The *ahem so called "pom-pom" CA has meshed up is still a bit big but is also the smallest plume they offer,thumbs down for them lol.
DDS would be.......
and your colour channel would be.......
lol minus the "colored stripe" forgot to blacken that