I googled and searched and could not find anything definite on this...

If I go from full-time to part-time, I am still entitled to all vacation hours accrued while I was full-time, correct? I can't see how it would be otherwise, but just wanted to make sure.

This depends on what you are talking about. Any vacation earned prior to going to part time cannot be legally forfeited. However if we are talking about vacation to be earned on a go forward basis, then it is legal for employers (on a go forward basis) to have part time employees earn vacation at a lesser rate, or not at all. A great many things can be legal on a go forward basis that are not legal retroactively.

http://www.dir.ca.gov/dlse/FAQ_Vacation.htm

I am only talking about vacation earned prior to going part-time (part-timers do not earn vacation at my company).

So it seems that I will still be paid all my accrued vacation hours even if my status becomes part-time.

That is correct.