sorry I think you have misunderstood the process: you "change the visa type" on Immigration from a tourist visa or visa-exempt entry to an initial 90 days Non-Imm-O Retirement visa on Immigration, for 2000 THB. It is number 9 on the list from this Immigration website. Click on number 9, a .pdf will open and show the requirements needed for the change. You however will need a Thai bank account with 800,000 THB already sitting in it for this application (!!) Without you already having a bank account, you cannot apply for the change" to the 90-days Non-Imm-O visa
not scandalous, just practical as long a cash will exist 😉. I bet you are the first one to whince when governments around the World discontinue cash payments
“My question is, while I’m there, will I be able to change my tourist visa to a 90 day visa to allow me to apply for a bank account”
This needs an explanation, because you like to do step two before you haven’t finished step one
You cannot apply for the “change of visa type” to a 90-days Non-Imm-O visa, without already having a Thai bank account.
And you cannot open a Thai bank account on a tourist visa or on a visa-exempt entry.
In order to get a bank account opened, you need to arrive on a 90-days Non-Imm-O Retirement Visa which you got issued in your home country.
On this visa you get stamped in for 90 days, and you are able to get a Thai bank account opened. You are free to use an agent service to smoothen and ease the process, it should cost around 5000 THB.
You needn’t apply for the 1-year extension, you can fly back before the 90-days stay permit expires. And return by next year on the same visa, again
and that's where the mind boggles: They use incorrect wording. They actually mean: if your stay permit is valid for less than one year, you can only get a 2-year renewal . . .It is the typical WRONG technical wording, DLT and Immigration are mixing up "visa" and "stay permit". These two authorities call a stay permit "a visa" and this is wrong. You ENTER Thailand on a visa, and then you are inside Thailand on a stay permit. If you go further, it means that all stay permits that got issued on a visa-exempt entry, on a tourist visa, on a METV, on a 90 days Non-Imm visa, and on a DTV, do NOT make you elegible for a 5-year renewal, because these stay permits are only for 60, 90 and 180 days - less than one year. I think what they meant to saywas - Only if you already got issued an Extension of the Stay Permit of exactly one year, you can apply for the 5-year renewal
the best is, never touch the 800,000 THB in your account. If your buddy did follow this simple rule, Bangkok Bank won't have any problem issuing the bank letter for Immigration confirming the 2-months seasoning of a minimum of 800,000 THB