Do I need to file a new TM30 after traveling to an island while registered in Hua Hin?

Whether you need to file a new TM30 when you come back from domestic travel at the immigration office in Hua Hin is something you should go ask the office. You can ask at Blu Port or at the main office.

MANY offices do not require you file a new TM30 when you travel domestically, BUT some do, so check with your office OR post on a Hua Hin F/B group to ask there..