It is a little odd that they locked it to Tactical - not sure why they did that.
I assume you'll be able to edit the appearance once you've aligned with either the Federation or the Klingons, but I haven't really tested that out, so maybe I'm wrong?
If you're looking for a bright side, you could use one of them to play around with unconventional combinations, like a Tactical officer with a science vessel or whatever.
Also: you've probably noticed by now that the Jem'Hadar faction drops you straight into the endgame (or at least the endgame at it was in 2018), so you may be better off playing your older character for the time being anyway.