Calling random altered functions based on an original function

Let's say that I have 10 altered functions for each original function, which all do the same, just different process of execution and maths. I want to call a random function out of the 10 altered functions instead of the original function every time the original function is supposed to be used in the code. How can I do that and avoid getting the 9 other altered functions compiled, that were not selected by random and won't be used?

This is to hand out a "different" build for each receiver with an unique signature. Only possible way of doing it, that I can think of, is to have a folder for each original function that holds 10 separate include files, for each altered function. This is kinda messy, but it's the only way that I can think of.

If there's an easier way of doing, what I want to achieve, please let me know. For example just adding junk code to the original function randomly on compiling - which would be even better, since it's dynamic. I just can't imagine of a way on how to do it.

Here's some pseudo: http://ift.tt/1Ewq7k9