I'm planning also to finish the O-A . So I'm leaving for holidays in Germany and I will come back on Non-O visa and then applying for extension based income/affidavit here in Phuket.
read the rules about O-A. All explained there. Every time, during the validity of the O-A visa , you will be stamped in for a full year at every entry. ( Watch your insurance validity!)
Leaving and returning shortly before your visa finish will give you the 2nd year of stay .Voilà . ( 2nd year needs a re-entry permit if you want to travel abroad)