OP Update: After getting numerous opinions that transferring at Chaeng Wattana is impossible if you got your stamps at a different office (including from lawyers and agents) and that Suvarnabhumi doesn't do it, I bit the bullet and flew to Koh Samui for the transfer. Arrived before it opened, had everything ready, officer told me it would take 7 days! This despite that there were very few people at the office (it's low season now) and plenty of staff. I told him I had flown down specifically for this, had to return to Bangkok the next day for urgent stuff, etc. etc. He said no. Said I should have done it at Chaeng Wattana!! I told him it's not possible, he said it is, they just have to call Samui office, etc. I begged relentlessly and finally he agreed to do it for pickup the next day. "You're going to make us work until midnight!" he said. But at least the ending was happy, this morning I showed up to pick it up and got it with the correct stamp transfers. As others have said, this kind of thing is idiotic. Visa and entry stamps are a NATIONAL matter, as is everything with Immigration. You are not getting a visa to Surat Thani province, you are getting a visa to the Kingdom of Thailand. Any office (especially the central office at the capital) should be able to transfer these stamps, it's not a question of issuing new ones, just moving the darn things from one passport to another. But instead they forced me to pay for a flight and hotel in Samui. Well, I guess I did my part to boost the tourist industry lol.