Can't offer you an official ruling, but if the spell changed your size category then it would say so, and also tell you the benefits you get from a change in size category.
No. The designers have been very consistent that's not allowed by the spell -- and it's in the FAQ (under an example for a dragon casting it on itself).
I was out side this quicky-mart when a telephone booth from the future came out of no where... & there was this Roofus guy, & we saved history! Then I went to the future on a intensive 18 month D&D 3e training session to make me the best DM in the world. I've got L33t chops now I tells ya' (L333t gawd I hate that word.) except for when it comes to enlarge & reduce, I failed that part of the futuristic DM trials.