Is it possible to get a re-entry permit at the border crossing point .

at Nong Khai your help please random

Is it possible to get a re-entry permit at the border crossing point .

at Nong Khai your help please random

Not sure about Nong Khai however you can go get one from Chiang mai immigration before you go

Best to get one in CM, even if they gave them at the border in the past does not mean that they will be doing it when you arrive there. The officer who does it just might be out sick, at a meeting or otherwise unavailable. Or they may have just stopped doing it the day before. It is a long way back to CM.

Please tell me, what is the legal difference between getting one in Chiangmai (immigration) and the one at the border?

None, assuming you can actually get one at the border. They didn't do them at Mae Hong Son immigration office last time I asked there. They come in single or multiple re-entry flavors.