I am also a PA resident! I applied to and interviewed at UCSD.
The rules about changing residency are very specific. You CANNOT change your residency status for tuition purpose! In other words, if you are only in the state of CA to obtain an education, you will not be able to get in-state tuition rates.
That being said, if you can demonstrate that you have a vested interest in changing your residency status, you should be able to get in-state tuition. For example, if you are married, and your spouse obtains a job in the state of California, and also changes his/her residency, then I think you would be justified in doing the same, and claiming in-state tuition.
Law2Doc probably has better insight into this. I'm certainly not an expert, but this is my understanding of the matter.