@Antonia ********
, yep, you still do three trips,
1 - to apply to change the visa from a tourist visa to a Non-O
2 - to go back in 14 days and get the Non-O stamped into your passport
3 - final trip to get the yearly extension of stay when you have 45 days or less left on the new 90 day stamp you got .
Whether you had a visa exempt entry or a tourist visa doesn't change the fact that you need to do three trips to pull it off :/ As long as you have 15 days or more left on your current stamp you can apply for the 90 day Non-O