Would it be possible to bend a 2 cm thick water clear polyester resin cast by applying heat ?

2cm is quite thick. What kind of radius do you want to apply?

Polyester resin, once completely hardened, is a three-dimensional network of one gigantic molecule, not a thermoplastic bunch of linear molecules like most household plastics. The heating and bending will cause some damage to the material, it will create cracks and broken chemical bonds. If this damage is visible depends on how much you bend the material.