As long as you can explain to immigration why you have a work extension from Bangkok but are living in Phang Nga. You won't be able to do a 90 day report in Bangkok unless you have a TM30 from Bangkok.
7 days might not be enough time to apply for a visa, if you mean you will only be there for 7 days. If you have a Thai wife or Thai child, you can get a visa based on that.