Will adding a, say, 2.0L Supercharger to my '12 challenger with the 3.6L technically make it a 5.6L?

 

No. the 3.6L is the displacement of the engine. Engine displacement is the swept volume of all the pistons inside the cylinders in a single movement from top dead center (TDC) to bottom dead center (BDC). Adding a supercharger does not change that. Displacement is figured on bore and stroke which PD boost does not change it simply compresses more air into the combustion chamber faster.