My question involves name change laws in the State of: California

My son is 17. I have not seen or spoken to him for over 6 years (ex moved and would not let me see him) now I have received a phone call from son asking that I ok him changing his name so his diploma will reflect the mom's boyfriend's last name.

Frankly, at this point it is a mute subject so why fight it - but my question is - if I ok this where does that leave my responsibility for child support? they are not wanting to do a formal adoption - just change his name.

Thank you for any help you can offer.