The problem is not what the OP used to make his model, but simply the rules of Tennogen... You can't alter the body mesh, at all.
DE also never took fan arts to make Deluxe skins (yet?)
So like @lukinu_u said (he's the only Octavia tennogen creator atm) if the OP is aiming to have his concept ingame, the best way is to make it following tennogen rules. Or as a fanart in the codex. Those are the two only realistic opportunities
BTW, OP, the helmet is looking cool imo you should try to upgrade it to DE standard and upload it as an alternate helmet