Hi Pal
I'm sorry, I dont know much about this but I just wanted to reply and help with whatever I know
. As far as I know as the Classical Guitars do not have Truss-Rod adjustments, the action cant be adjusted. And hence if your Guitar is designed (or made) for Medium Gauge strings, then putting Heavier strings would cause extra pressure on the Guitar. Hence this may lead to either the Bowing of the neck or Harm the area where the Bridge is Placed (on the Top of the Guitar)
Sorry if this advice is not useful, Just wanted to help
Take care and have a great day, pal
Kindest and Warmest Regards
Kush