There are three possibilities using the console:
Advancing your level
The UESP page for console commands suggests using
advlevel to increase your character's level, which will then increase the difficulty of enemies. Since
advlevel doesn't give you more perk points or health, stamina, or magicka, it effectively increases the difficulty of the the game.
So, to increase the difficulty of the game by one level, open the console and do:
Repeating the command will increase the difficulty several notches. However, there's some belief level scaling stops at level 54 or so, so this might not help.
Changing your attack damage multiplier
Consider from the the answer to the other question about what effect difficulty has on your character:
Difficulty | Damage Dealt | Damage Taken
Novice | x2 | x0.5
Apprentice | x1.5 | x0.75
Adept | x1 | x1
Expert | x0.75 | x1.5
Master | x0.5 | x2
If you want to pump up the difficulty another level (let's call it Grand Master), you'd want to cut your damage dealt by another 0.25x and the damage taken by 0.5x:
Gd. Master | x0.25 | x2.5
You can achieve the first part (damage dealt) the console to modify your attack damage modifier. Effectively, all you should need to do is half your attack damage multiplier using
player.setav AttackDamageMult 0.5
To change the damage taken, you'll need to change your health or your resistances, which is explained in the next section.
Changing your other stats
You can get finer control by modifying your player's actor value indices, like changing your melee and unarmed damage or your resistannces.
First, get the current value using
Then, set your damage multiplier to something else using
player.setav [Insert half the value of your current MeleeDamage here]
player.setav [Insert half the value of your current UnarmedDamage here]
getav again, record the values for the following resistances:
Halve the values you get here, and set them to the new values using
Alternatively, you could just set your current total health to half its current value:
player.setav Health [Insert half of your current total health here]
Setting your player scale
yx. mentioned in the comments that people have found
setscale will affect the amount of damage you do: decreasing this value should decrease the amount of damage you do. However, it also affects other things not normally affected by difficulty, including your physical size and your run speed.
You can find out your current scale by using
setav just lowers your base stats: your items will wind up making the effects of the modification less potent. Changes to stats modified with
setav also persist after reloading. If you want to force your stats to take a certain value, regardless of what items you have (and have it persist through sessions), use