@Bonnie ***********
you said your 90 day report is DUE. Some immigration offices won't let you get a new extension until you've filed a 90 day report.
BUT, yep, your reasoning makes sense..
Go to Chaengwattana and move the stamps, TRY to apply for your extension and then (if you do get it) go file your 90 day report..
AND
if you get the stamps moved but they don't let you apply for your extension at least you'll be filing a 90 day report on the new passport and then you can go back and get the extension.
Anyway you slice it, you're gonna go to BOTH C/W and MTT..