All the code is in the Panda source tree. You can look at ServerRepository and see what it imports.
I doubt you would be able to implement a new server without any changes to your client code at all, but probably the changes would be minimal. ServerRepository.py is designed to work more-or-less like Disney’s ultra-efficient OTP server, after all, and programs that are written for the one would probably run with only minimal changes on the other.
David