He asked if he can do that on entering Thailand and that is not possible. You might be able to convert after you are in Thailand but that was not the question.
Well I have never heard that and have been here 36 years. So I asked and got this answer: No, you cannot change a tourist visa to a Non-O visa at arrival in Thailand, but you can apply for a change of visa type while you are in Thailand on a tourist visa. To do this, you must apply at an immigration office in Thailand, have at least 15 days remaining on your current visa, and wait for the approval process there. The application must be made before your initial visa expires.
Very simple. Simply go to the bank as long as you have a NON O visa. You need that visa anyway to apply for the visa. But you can not apply for the visa unless you have less than 30 days left of the 90 day visa.