This would get you some extra money through the C-store. If you level up a character to Captain or so and then realize you would rather have another species, there is no way to go about doing that. Would you consider a species-changing token in the C-store?
At least a few of the missions involve using holo projectors for disguises so your idea could appear in that form if there's enough practical interest to do so. Small c-store purchase for holo disguise item.
Not very 'canon' for permanent change in character species however...
I like this idea / request. I choose an Andorian when I started (thinking I could later change) only to realize that I couldn't. I did post a similar request in another thread (I forget which one now) but yeah... It would be nice if they allowed us either to create a second captain (for the same account) or to edit our species along with our attire and appearance.