How can I switch from a Non-B business visa to a DTV in Thailand?

The process of switching from a Non-B business visa to a DTV can be complicated. Once on a visa, cancellation is not possible; however, if on an extension of stay, one can cancel the work permit and proof of cancellation can be used at immigration to exit Thailand and apply for a DTV visa from outside the country. It's important to consider how a re-entry permit on the Non-B may affect this process.