@Dieter *********
We already exchanged each other in another group.
***you cannot get a Thai bank account opened on a touristic entry, and the DTV is a “tourist visa-class”
*** you cannot do the “change of visa type” from a DTV to a 90-days Non-Imm-O Visa.
The DTV is a multi-entry 5-year visa. It needs to get cancelled before you will be able to apply for another visa or the “change of visa type”. You cannot apply for a new visa as long as you are on a still valid visa. And since the DTV is a multi-entry visa type, you just cannot invalidate it by exiting Thailand without a re-entry permit.
***you will need to ask the embassy that issued your DTV if they are willing to invalidate it
*** You have you can use the 5-years DTV fully up, make a border bounce every 180 days, and just let the visa validity expire, before you apply for a 90-days Non-Imm-O visa either anywhere in the World, or inside Thailand on Immigration by applying for the “change of visa type”