As suggested by Connor and others, this goal is for an armband slot. This would not only make it so that the nice Volkssturm civilian uniforms could be worn without armbands, it'd allow armbands to be worn with any uniform!

This goal will require both a new slot in the inventory as well as custom rendering to handle the rendering of the item in that slot. It will also have a lot of busy work separating armbands from uniforms into their own items.

If this goal is completed, it'll likely be easier to add other slots too, such as an equipment slot that would separate equipment from the uniform.