@Jason ********
In case you are planning to do the “change of visa type” from a Tourist visa or visa-exempt to a Non-Imm-O retirement Visa, you can only get the single entry 90 days type, NOT the multi entry type.
You will have to apply for the 1-year extension of stay 30 days before the 90 days are up. . . in order to apply for the change, you will need a minimum of 15 days left on your admitted stay stamp, and you either need 800.000.- THB in your Thai bank account along with the proof it came from abroad, OR an Embassy affidavit of a monthly income (if your embassy issues them).
You will receive a “90-days single entry Non-Imm-O retirement visa”, first 14 days “under consideration”.15 days later you can pick up your visa stamp. Then as soon as the 800K have been sitting in your account for 2 months, you can apply for the “1-year extension of stay based on retirement”