You can't choose background in game, its just bound to that button so that A. Switching languages doesn't screw up everything again, and B. for testing purposes.
Stick doesn't do anything because I don't have sprites.
I've stated multiple times that store-bought vs wild are not setup atm because I was in the middle of editing the UI and it would have been pointless to set it up just to break it in the next version.
The type of baby produced is based on a dice roll and I haven't messed with that code pretty much ever, though if you're talking about Cirno, thats different. Cirno has her own settings that aren't shared by the other yukkuri and I didn't have a chance to standardize her/ I wanted to test some status effects and inheritance.
And I get to be as cryptic and mysterious as I want until you find someone better to be your code monkey.