@Marc *******
WOW, change your mind, how did you made that up?
You can buy the Non Immigrant ED visa in two different scenario.
1 Outside Thailand and than it is a SINGLE entry visa, which can be used once to get 90 days of stay and will be stamped USED, no need to cancel it later.
2. Inside Thailand as a NON entry visa, you get a new 90 days of stay.
NO need to cancel the visa if you leave.
IF you want to travel and keep the 90 days alive, you use a Re-Entry Permit, sitill no need to cancel your used and invalid visa.
NOW the problem start.
IF you visit Immigration for an Extension of Stay, one of the documents you sign is the one I showed STM2.
With this form you sign you understand and acknowldge the rules and regulations.