I did a little digging around (i'm sorry that was a bad joke, but with a name like geodude the opportunity was too tantalizing), and NSF fellowships are transferable between "GRFP institutions" - which I think means a higher education accredited university, so I don't think I have trouble there. However, I think I fall into trouble if I want to switch from something like space physics into something like astrophysics, particle physics, or cosmology because these may be deemed as major field of study changes.
So I guess I'm stuck in space physics, which is kind of a shame because space physics is really more like using a little physics here and there but just enough to study the sun-earth environment, and I always thought I was more into physics like solving differential equations, writing code, being in a lab and using cool lasers, looking at blackholes, making superconductors, or researching Bose-Einstein condensates or gravity waves, or accelerating particles to TeVs or something like that.
I'm kind of torn, because on the one hand, how does one say "no" to a prestigeous fellowship like the NSF fellowship, which more than pays for my graduate schooling and then some, but on the other hand I just worry that if my heart's not in it then i'm not gonna have the passion to keep going after a while.
And to top it all off, I feel a little sour about the entire experience. Both schools basically rejected me, and only accepted me after I got this fellowship, so its pretty apparent that I am not attending UCLA on merit (UCLA didn't believe I could make it in their program in the first place), but merely on the fact that I can pay for myself...which is a pretty huge hit on my confidence going in.
In any sense, this next year is definitely going to be interesting.