Question about good design: overriding functions, function parameters or similar

You cant give a function to an entity. It just exists as a function that you can call wherever it has scope.

But from the sounds of your question you're a software programmer, and your hardware architecture sounds like a software program. This will yield terrible results in an FPGA if it even works at all.

My Advise - start again, and draw your circuit (not functions) on a peice of paper outlining where all the things like memories, state machines etc are in your processing pipeline.