Can I change my NON-O visa to another type after 3 months in Thailand?

You can’t change the “reason” the visa was issued for, after you applied for the “change of visa type” inside Thailand and received the 90 days Non-Imm-O visa.

You have two options:

*** you keep following the path to apply for the “1-year extension of stay” based on the reason the 90-days Non-Imm-O was issued for. You will need to fulfill the required financial proof.

After getting stamped the extension, you can change the “reason” of the extension, like from “retirement” to “married to a Thai wife” or “employment” . . . if you can fulfill the requirements

*** you can exit Thailand, and re-enter visa exempt. You will get stamped in for 30 days. Visit Immigration immediately and apply for the “change” from the visa-exempt entry to a 90-days Non-Imm-O visa based on the reason you want it for. You will need to fulfill the requirements specified for this reason.

*** the requirements are listed on the Immigration website, if you google “change of visa type Thailand”

No,

you can only extend the original visa for the reason that you obtained the visa, for the first extension.

The following year you can apply to change the reason for extension depending on what it is you are trying to do.