This might set a record for dumbest mod I've uploaded.

There is a value called difficulty in Payday 2. However, it is not the difficulty you are probably thinking of, such as Overkill or Death Wish. Instead, it is a value from 0% to 100%. This value is used to set certain other values in assaults, as a way of the assaults ramping up.

For example:

sustain_duration_max = {
			40,
			120,
			160
		},

Difficulty tells the game which of these values to use. At 0% (impossible, only occurs in stealth) an assault will have 40 max seconds on its sustain duration. At 100%, it will be 160 max seconds. At 50%, it will be 120 seconds. If you have a diff value of say, 75%, then it will take the value between the two (140)

Difficulty normally starts at 0% in stealth, goes to 50% for the first assault, goes to 75% for the second assault, then stays at 100% past that (however, some maps are exceptions to this). By forcing this value to always 100%, we are effectively starting on the third assault. I don't know how much of an impact this is going to make, but it does change things to be harder.

Examples of things that appear to be affected by difficulty:

Assault Duration (sustain phase)
Assault Pool
Spawn Cap
Assault Delay

If you want to read more about how all of this works, search "Police Tasks and Assault Waves" on The Long Guide here. Note that difficulty is what is used to determine when assaults actually start, but there are instances where no spawn points will be enabled yet. As a result you'll be sitting during an assault with no enemies spawning until they would kick in normally. An example of this is Hotline Miami 1.

Not sure how this affects stealth (then again why would you even use this for stealthing xd). If this still isn't hard enough for you I would recommend trying Full Speed Swarm to make the enemy AI actually do something.

tl;dr you start on the hardest assault wave possible instead of waiting through the first two.