So to launch game with different difficulty levels, game length or game mode, you need to alter the mapswitch URL.

To launch with Endless mode:
Open KF-BioticsLab?Game=KFGameContent.KFGameInfo_Endless?Mutator=KF2Bots.KF2BotsMut

Versus mode: (NOTE that all bots will all spawn as human side players and will rekt you with their aimbot)
Open KF-BioticsLab?Game=KFGameContent.KFGameInfo_VersusSurvival?Mutator=KF2Bots.KF2BotsMut

To launch with different difficulty levels, also append ?Difficulty=X to the URL where X stands for:
0 = normal
1 = hard
2 = suicidal
3 = hell on earth
So for example to start regular survival game with HoE:
Open KF-BioticsLab?Mutator=KF2Bots.KF2BotsMut?Difficulty=3

Then to launch with different game length settings, add ?GameLength=X where X stands for:
0 = short
1 = medium
2 = long
To launch long game on HoE:
Open KF-BioticsLab?Mutator=KF2Bots.KF2BotsMut?Difficulty=3?GameLength=2