Glen Shkolar There is nothing special about an Ed Visa Extension versus any Extension that must ordinarily be cancelled such as a B Visa - leave without an Reentry Permit while on a B Visa Extension or O visa Extension (retirement)... and the Extension is cancelled. Not properly done but it is cancelled. Ed Visa Extensions are not Magic
Theses Consulates spoken of here, Portland, New Orleans and add those in (Dallas, Miami, Atlanta I believe and Honolulu) Are not standard Thai Consulates. These offices are contractors - most often not Thai Citizens. Officially they are termed: Royal Thai Honorary Consul General.
They used to have nearly full function but are quite limited in their powers these days. The Thai Govt. cut way back starting about two years ago