Legal Question in Family Law in California

Well before and after marriage it is already the law that it is separate property. What you mean is that during marriage can a person can opt out of the community property system so everything is separate property, yes.

Waiving spousal support? These kinds of agreements have extra conditions that need to be met to be valid but a court could still find the waiver of spousal support unconscionable.

Note some people think they'll make more money and sometimes the other spouse actually does....

after marriage = divorced

If you are a party to a potential prenuptial agreement, I strongly urge you to seek the advice of an attorney to review the entire agreement. Many of these agreements executed today are not valid unless both spouses had the opportunity to have the document reviewed by their own attorney, or waived that right, in writing, along with other requirements.