Making a bigger transfomer core by stacking multiple smaller cores
As long as there is no significant mechanical differences from the magnetic viewpoint it should be much the same. Core laminations exist to limit eddy currents, and stacking cores is just separating some of the lamination groups. 

Considerations:

It's likely that there will be slightly more gap at such boundaries if care is not taken to compress them together well. 

Glueing core groups may allow a small gap due to glue thickness - and an air gape is vastly larger magnetically than the same distance in core material, so every effort must be taken to eliminate such possibilities. 

Noise and vibration can occur if the core groups are able to move relative to each other more freely than can tight packed laminations.