Unfortunately
Paulaf I didn't book these seats at doors 2&3. I just looked longingly at those who did......note to self for the next time I travel Monarch
The A300 is nothing more than a flying "cash cow" for whichever airline operates it....and in Monarch's case to the max capacity the CAA will allow in the summer season.
On the Prevesa flight, as Avionka says, it is only 3 hours long. Monarch (or any other carrier) will not loose sleep over the customer experience either way.......
I would say contact Monarch either via their website, if it has the capacity to book seats at exit row doors, or phone them.
Be aware though that many airlines don't allow you to do this until you get to check in. As CC I understand why. Not sure what Monarch's policy is on this.
Hope this helps.......sort of!