Can I transfer my visa stamp from an old passport to a new one in Thailand?

I just got a new passport issued last week in CM. The last 30 day visa extension stamp was done in Maehongson. My next exit out of the country will either be by land to Malaysia or probably a flight out of BKK to Australia. I was planning on getting on a bus tonight to BKK, but I read somewhere that there's a chance the stamp can only be transferred at the immigration office where it was issued which would be in Pai, Maehongson where I had it extended. It's Saturday today so I could go to Pai tonight and go to the office on Monday to be safe. However, I'm also reading in some places that I need a statement from my embassy verifying the validity of the passport before they transfer the visa stamp, but unfortunately it's Saturday and the embassy is closed. So two questions here, and I'm American if that makes any difference. Trying to get this done quick before any more borders close down. Any help would be great guys! Thanks