You could potentially save all of the variables, using easy save, your game uses in an editable txt file (no encryption key) and then load that file at the start when your game is loaded (this is how I'm doing it right now).
This would allow the player to change values to make the game harder or easier (like more hp, more damage per hit, faster weapons cd's, etc.).
These however are very small 'mod' options, but there's the possibility to expand on this further, if you were to generate, let's say, completely new weapon systems through text files, this however is above me for the moment, but I'm sure it's possible.