Will changing my character's gender with the "showracemenu" command screw my game up in any way? level reset, stat/skill reset, quest progress.. those kind of things.

Yes, the Chargen menu can cause all kinds of issues for your character. It is not guaranteed to hose, but the big problems that may happen do not show up until you save and reload the character the next time.

Here is what you do, make a forked save first. Load that save, use the menu, make your changes. Then, save the game, new slot or overwrite your forked save, then exit out of the game. Reload the game, reload the save and look at your character's stats. If it is hosed, reload the save from before the menu and try again. Do not try to use the console to fix skills and perks, it will only get worse.

So there is a chance it -may- work?

sure it may work. Make sure you create the forked save so you can pretend it never happened if something goes wrong. Doesnt hurt to try, right?

But like, can it "break" things for me later in the game? For example let's say it works, but then something goes horribly wrong hours/days from then? Or even weeks later xD

Nah, if its going to do any damage, it will be obvious at the next reload.

EDIT: Seems to be working. My attributes, Skills, stats, Items and spells all appear to be correct. Thanks for helping you two.