Can a Lawyer in Thailand do the paper work on your behalf if you are not in that part of the country or abroad, when the actual chanote changes over, or does the new owner have to physically be there?

If so, what authorization does the person have to give the lawyer to act on their behalf ?

A lawyer or indeed any individual can do if they have power of attorney, there are standard power of attorney forms available from the land office for this purpose.

The POA forms must be notarized in the other country by the Thai embassy/consulate there.

P.O.A....you can give to anyone, if you are here, do it befor you leave

Just make sure that it is a limited power of attorney, detailing specific actions that the lawyer or individual can perform on your behalf