Can I switch my visa type from a Non-B to a DTV while living in Thailand, and what steps should I take?

Finish out your current non B .. the work permit is attached so it is automatically cancelled.. then go out to do the DTV ☺️

You school needs to cancel your work permit. You them leave Thailand and your non b will be canceled also. The visa is tied to the work permit. You then apply for your DTV and there will be no problem. That's how l did it. DTV in Vientiane 3 days pick up new DTV and bus to udon Thani same day no questions asked from immagration at border. Stamp 180 days

You can not "just leave". They probably would not even let you out at the border. You have to cancel the "Non B visa". That is funnily done with an "extension of stay" form, where you give as reason "visa termination/cancelation". Then you get a 7 days extension.

Yes, some nitpickers will point out "the vis already USED. You are on an extension of stay, based on an Non B visa" - no worries, the immigration office knows what you mean with "cancel work visa, please!"

Regarding the work permit, I do not know. It is basically automatically void, when the visa/extension is canceled. However you are (and your employer is) supposed to inform the administrations in less than 10 or so days. You have to check that.

As long as you're not tempted to work for a Thai entity and are prepared to answer immigration questions honestly (if any), that shouldn't be an issue.

I assume you're not actually on a visa but an extension of stay. Cancel your work permit, take the documentation from that and cancel your extension of stay, then leave Thailand and go and apply for the DTV in your chosen location

I'm no expert, but I think being employed by a thai company is going to be a problem. I'm sure someone will be alone soon that knows better

Edit.

After reading your post again, I take it you won't be mentioning the Thai company when applying so probably all be fine. Will your bank statement show thai income?