@Max ************
the whole process is only possible if you accept the overall wrong wording of Thai Immigration. . . . . „But a 60-days tourist visa and the 90 days Non-immigrant O are a visa. That's why it's called "Change of Visa" at immigration”
That’s where you fail!
After you entered Thailand, you have no more visa.
That’s why Immigration will just “change” your 60-days stay permit status to a “90-days Non-Imm-O visa”
They don’t change from a visa to another visa. They just change your stay permit status.
And since for Thai Immigration and their bad and wrong English, there is no difference between a visa and a stay permit, they confuse people like you.