Sure I don't have the US keyboard checked.. I don't remember if I had to jump through any hoops to uncheck it, because I chose Castillian as the primary language at install so I got the Spanish keyboard as default, but looking at the International preferences I am allowed to uncheck the Spanish keyboard.. (I do have other keyboard layouts active such as Norwegian)
I thought if you checked another Roman keyboard layout you could switch the first Roman keyboard layout.. sorry if I can't help more than that. I just know it should be possible to change keyboard layouts.