Regarding the ability to edit the player file, it's relatively simple to do and the game's datafile contains documents detailing what each player stat relates to in the .csv file. It does not allow you to edit the player skill values directly, but to quote from the editors guide in the datafile:
Essentially, you are able to edit the player file to make certain players much better or worse than in reality and the game also has an in-built randomness slider you can turn up or down to add even more replayabiity and "what-ifery" to the game.