Traditionally games have used adjustments to the relative strength of opponents to alter the challenge presented by encounters. These adjustments frequently take the form of alterations of hit points, the probability of successful hits, and the damage inflicted by hits. While these sorts of adjustments certainly have their place there are other ways to make games more or less difficult. Options like a hardcoe mode, which place more realistic demands upon the PC, force players to think about a wide range of concerns as they plan their activities. I would like to propose another way of allowing the player to adjusting the challenge posed by the game; altering the spawn lists. By giving the player control over the lists used to place opponents in the game they would be empowered to tailor their game to meet their desires. The simplest way this could be accomplished would be by adding or subtracting from the number used to determine the level list being used. Some desiring an easy game could opt to only face opponents several levels below their current level while those seeking a greater challenge would used a level list several levels above their current level. Thus, at this higher difficulty level players would face a greater variety of opponents. A more complex system might adjust the frequency at which high level opponents appear. Alongside the traditional method adjusting the difficulty this approach would allow for a vast array of possible combinations, allowing players to personalize their experiences.
As an added bonus, in its simplest for this system would require only a few lines of code, beyond adding a slider in the game settings. Thus it could be easily implemented without a trade off elsewhere in the game.

What do you think of this idea?
Are there other ways you think that the difficulty of the game could be adjusted by players to suit their tastes?