Well no, the representation of game state and input have to remain the same ^1. I guess in lisp you could more easily write a function that maps the previous representation into the new one.

Here is an example of what kind of interactive code reloading I have in mind: https://www.youtube.com/watch?v=xrUSrVvB21c

Admittedly it is more of a hack than in a Common Lisp system, but still.

1) EDIT: At least in the most simple design. Nothing prevents you from optionally stopping the simulation, serialize a snapshot of the sate to disk, change the representation of complex numbers or whatever, together with the data serialization routines and continue.