I see you don't have 400k in a bank account. Are you planning to arrange that? You should arrange it ASAP, and then you can stay for a year hassle free. All of this COVID business will go on for a long time yet. Get whatever extension you can in the mean time. Looks like a further 60 day is possible for people now.
Yes so if he does not have the 65k a month would they not expect a 400k minimum and then the 800k 2 months before ? I am not sure how that works when switching from 65k a month method.....to the 800k / 400k method.....
As James says, a visa can't be transferred. Carry both until it is time to get a new one, or if an extension of stay is applied for, that can be stamped in the new passport later.
Why is it belittling to follow a process to get a visa to have the privilege of staying in Thailand? I hope they don't ask for tea money when they visit. Not sure if that happens much. Good luck.