definitely. But you can choose any place (where you have to remain) to do that. Whether you apply from Vientiane, Hanoi or Manila, the same people deal with your application.
As the process is online, the place is not really relevant. Everything depends on your application. I saw some people get their non-O visa the same week in Vientiane and some wait for it more than two weeks. The staff in a particular place help but don't decide.
An ED visa is for studying in a school Thailand with a curriculum and a time table. If you actually stay abroad, I guess you will need another category of visa for your next visit to Thailand.
Your future husband should not be afraid to spend some time in a neighboring country to apply for the visa which will fit his new situation after he gets married. But, before that, he can do an extension of 30 days.
The agent is right. The category of visa you have stipulates that you can't extend it any longer. Then you would have to apply for a change of category of visa, but that must be done 3-4 weeks before the end of your present visa. You have to leave the country and apply for a visa fitting your new situation.
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