hello mastergridd welcome back here
yes you can ammend your passport whilst here in the UK (Philippine Embassy in the United Kingdom at 6 Suffolk Street, London, SW1Y 4HG)
and will not have a problem with the visa as long as you got the original supporting documents with you like marriage license,birth certificate.
http://www.philembassy-uk.org/
http://filipinaroses.com/archive/index.php/t-8078.html
