I just saw a post on Twitter that listed the genders supported by the Infinity Engine, and a few of them (Both, Neither, and Other) look like they might be appropriate for the main character.

Are there any mods to enable those genders for the protagonist? (For any IE game)

I don't think so. It sounds like the gender thing is part of some game mechanics. In the big picture gender in the IE games (the choice you make at character creation) is superficial and doesn't really change much aside from a few quests and dialogue. Changing something like what you mentioned might alter how the game works.

Yeah, gender is used for in-game mechanics in out-of-the-box ways you would never suspect. It would be a bad move if it were used by modders, which probably explains why they haven't already done so.

Do you have any specific details?

(Some of the other genders on the list are things like Summoned, Illusionary, and Imprisoned_Summoned, which actually look like some things used by the engine. By the way, why aren't there spells that create illusionary creatures to fight for the party?)

It would probably be redundant. The only difference between illusory creatures and ones created by summon monster is the illusions wouldn't do any damage. In P&P you can do all sorts of things with illusions of monsters, but in the context of the IE games it wouldn't really work.

I don't have full technical details, no. However, the engine uses gender.ids for controlling/dispelling summons, illusions etc. Without very specific details on how this is implemented a modder would be playing with fire.