No, you cannot change the type of visa. If you have a single entry visa/extension you can buy a reentry permit either at immigration or at the airport.
Reentry permit allows you to leave and reenter without affecting your single entry visa. 1 reentry is 1000 baht, multiple is 3800 baht.
Sorry Tony, his post was a complaint, not a question asking what he should put in the box. People ask what to put for questions that aren't applicable to them all the time. He just wanted to complain.
I also don't maintain an address in the US, but like most of the other questions on the visa and thaipass application, it doesn't matter what you put, just put anything.
Filing as married and claiming someone as a dependant are 2 different things. Generally beneficial to file as married as it doubles the income threshold for each tax bracket.