The Name Equality Act of 2007 allows couples applying for a California marriage license to change their middle or last names as a result of their marriage ceremony being completed/celebrated.
It will be cheaper and time efficient to make this decision at the time you obtain your California marriage license because it can be noted at the bottom of the license in Section 30A-31C.
Changing your name after your marriage license is issued (and before you are married) will require the purchase of a new license. Changing a name AFTER your marriage ceremony has already been performed requires a court order and can be a lengthy, expensive process.
Bottomline: give some serious thought to what your married legal names will be BEFORE applying for a license and save yourself both time and money!