Can I change the return date on my Thai re-entry visa after signing the form?

You cannot change the specific return date on your re-entry visa after you have signed the form; you must put an imagined travel date since leaving it blank is not allowed. The re-entry permit is valid until your extension of stay expires, allowing you to return any time before that validity date. If your plans change, you must return according to your new plan, but do so before the last 'Admitted to Stay' date in your passport to avoid losing your extension and re-entry permit.