❔ Adding Polymorphism to a program

I have project for school and I must use Polymorphism but I have already written everything and it works and to add Polymorphism where few classes use 1 base class would require to change a lot. What if I use 1 new "base" class which would get inhereted by my already made class and I would add Polymorphism functionality to it? Would this still count as having Polymorphism?