@Dan ************
the OA is a retirement visa so no, you cannot "convert" the OA to permanent residence. You can't convert anything to permanent residence.
One of the requirements is to work in Thailand and pay taxes for multiple years before you can even apply, and then it takes more years after that to process. How would someone on a work restricted visa work and pay taxes?
You making Permanent Residence sound so simple marks you out as knowing nothing about the process. There's a reason very, very few people have it.