Can I switch from a work permit extension to a retiree extension in Thailand while meeting the financial requirements for both myself and my wife as a dependent?

So you will cancel your current extension (and you wife will cancel hers too) with documentation from your employer and then immediately apply for a year extension based on being over 50 (retirement) and your wife will immediately apply for an extension based on being "trailing spouse".

Only YOU will require the 800K baht banked in a thai bank account in your name only for 2 months before you APPLY for the year extension.

The 800K baht has to stay in the account for 3 months after the extension is granted, and then the balance can't go below 400K baht the rest of the year <- right up until you apply for your next yearly extension using monthly income method by international transfers by transferring in to the country a minimum of 65K baht a month, each month, every month for the previous 12 months

In essence, you meet the seasoning requirements for the year extension you're on using banked money method AND you begin to transfer in the 65K baht a month each month for the NEXT yearly extension you will apply for using monthly income by international transfer method.