Presently I have a B visa extension from my business and work permit

I would like to change from B to O visa extension due to qualifying through my legal child

I know and I do have court order, registration for my child and 400,000 bth in the bank for min of 3 month

My question is that is this possible without leaving country and will the immigration will change my extension assuming I have all the required documents

additionally can I keep y existing work permit or will I lose it and have to reapply

If you have all of the documents you can do it at your local immigration office without leaving the country. I did it a few years ago. I first extended my "B" for 60 dyas because I had a Thai wife since I didn't have all of the paperwork in order and then went to extend it for 1 year for marriage. I actually walked out with a retirement extension since I qualified, it was easier for immigration and me, and I did not intend to work.

You said:

"additionally can I keep y existing work permit or will I lose it and have to reapply"

I didn't think you could hold a marriage extension and have a work permit at the same time. Someone who knows about that will reply. I've never been in either situation.

Wayned knows all, but I didn't see him address that part.

Good luck.

You don't change visas since in reality you don't have a visa. You simply change the reason for your extension for working to one based upon marriage marriage.

You will not be able to change until your current extension ends or you stop working.

If are working and have a income of 40k baht or more income proven by tax payments and your work permit to prove you are working legally you it for the extension.

If you your job ends you would need a letter from employer stating the date it ends. On that date you would need the 400 baht to be on the bank for 60 days and all the required documents for an extension of stay based upon marriage.

You said:

"additionally can I keep y existing work permit or will I lose it and have to reapply"

I didn't think you could hold a marriage extension and have a work permit at the same time. Someone who knows about that will reply. I've never been in either situation.

Wayned knows all, but I didn't see him address that part.

Good luck.

He can continue working with a work permit with an extension of stay based upon marriage or even a non-o visa.