I know a couple of guys who are on Non-Imm OAs & pay an agent an extra 2,500 THB to get around the insurance requirements (on top of the 12,500 THB normally charged to get around the finance requirements)
I've never heard of an agent being able to convert a Non-Imm OA to a Non-Imm O in-country & obviously it's been difficult for people to leave the country for the past couple of years (especially when, up until quite recently, you needed medical insurance to get back in & I've never heard of anybody being able to get around that)..
Of the 2, 1 guy is going to pay his agent 15K again end of this month to get his extension & then do a border run, come back on a Visa Exempt & convert to a Non-IMM O next year, the other is planning to do the border run before his extension expires in October.
Fingers crossed for them (& lots of other guys) that they don't mandate Non-IMM O's have the same Health Insurance, I personally don't understand why immigration hasn't done this, which is one of the main reasons I signed up for Health Insurance whilst I was still <55 & could get a reasonably priced policy.
Worth mentioning that both guys come from countries (UK* & Canada) where they can get free medical treatment at home & both plan on going home if they were struck down with a costly disease or when they hit an age where they feel it's just a matter of time before they get one, both also have accident insurance so they've done their best (outside of having medical insurance) to cover themselves but if they were to suffer a stroke, heart attack etc... they would probably end up relying on the charity of family & friends or Go-Fund me.
*NB technically us guys from the UK lose access to the NHS when we become Expats BUT we get it back on the day we return if we can show that we're repatriating.