I registered as an overseas voter in 2010 but I know I will be in the Philippines come 13 May 2013. Can I vote in the 2013 elections in the Philippines?

Yes, you have to file a Letter-Request for Transfer of Registration Record (OAVF No. 1B) before your Embassy or Consulate or before the COAV in Manila. Upon receipt of approval of the request for transfer of registration record, you have to go to the office of your local election officer and submit CEF 1B (Local Application for Transfer) and have your biometrics taken.

Source: http://dfa-oavs.gov.ph/index.php/2012-09-21-01-40-54/oav-primer