@Law *******
Sorry, but you don’t extend any Non-O visa inside Thailand
*** you arrive on a 90-days Non-Imm-O retirement visa which you got issued outside of Thailand
*** you get stamped in for a 90-days stay permit
*** the Non-Imm-O visa becomes invalid as soon as you receive the “admitted stay” stamp upon entry
*** on Immigration, you will apply for the “1-year Extension of the Stay Permit”
You will be living in Thailand on a “stay permit”, not on a visa