I have a type ‘C’ Schengen visa valid from June 9 2019 - June 8 2020. In September, I will be going to Thessaloniki in Greece to observe in a hospital (I work in healthcare), supposedly for 6 months. The Greek consul in my country advised me to use my current Schengen visa for this trip.
However, I know the maximum length of stay is 90 days.
My question is, while in Greece, can I apply for an extension to the 90-day stay? I know you can apply to extend if your visa is expiring, but mine is not. I just want to extend the length of stay.