Basically stealing veteran29's improved idea after my wish, but here is the idea:
In the Launcher, have buttons in the Preset list (probably + and - icon) to append/subtract the Mods/DLCs in the preset.
For instance:

1. Have a loaded Mods
   • Currently it lists ModA, ModB, DLCA
2. Append a Preset
   • The preset has ModC, ModD
3. Results 4 Mods and 1 DLC
   • Now it loads ModA, ModB, ModC, ModD, DLCA

Or,

1. Have a loaded Mods
   • Currently it lists ModA, ModB, DLCA
2. Subtract a Preset
   • The preset has ModA, DLCA
3. Results 1 Mod
   • Now it loads ModB

Basically the idea is “Okay I want to add the entire CUP with one click!” and vice versa.