How to calculate the ratings when a mains-rated transformer is used in a SMPS?
If this is a ferrite core transformer, maybe you could get comething out of it, but if you have a laminated core transformer, the eddy currents will cause too much trouble. Would not be a practical design.

There is a paper detailing high frequency bahaviour of laminated core inductors.

You could probably get some useful info out of it.