Completing the story missions will that increases the difficulty (minimum skulls) of the planets, and once unlocked can never go back down in difficulty.
One such mission is when you get the Argo. Prior to this, there are planets with half-skull to 1.5 skulls. After this, the planet minimum skulls start at 2.
There is a to tweak this to not increase the difficulty.
The same mod also has the ability to generate "up to" 10 new missions. But the missions are tied to faction ratings if they can be done.
My campaign as after doing the Panzyr, so all planets are at 2 skulls minimum.
However, with the mod, I can find contracts from half-skull to 4.5 skulls.
I did a 3 skull mission last night and it was hard, but I lived.
I have
55t Shadowhawk 2xSRM6+++, SRM4, 1ML;
50t Centuroin with 2 LRM20+++;
60t Dragon 2xSRM6, 1ML, 4MG;
65t Jagger with AC20+++, 1ML, 4MG.
I fought 2 lances: Orion, Enforcer, Griffin, Caraphract;
and another lance flanking Vindicator, Wolverine, Shadowhawk, and Commando.
Since I stopped pursuing the mission, it has become samey--travel to the next star, check store, do contracts to pay monthly expense.
Still, I could not find the +++ weapons that I found early in the campaign.
And I am slowly getting higher ton mech salvage.
I also hired 4 backup mechwarriors in my roster.
1 to mimic the skills of my main Gun [5] [8], Gut [5].
Behemoth: Pilot [5], Gut [5] [8].
1 to replace Behemoth: Gun [5], Gut [5] [8] instead. I prefer multi-shot to evasive.
Dekker and Medusa are both scout/recon: Pilot [5] [8], Tac [5].
Glitch is my missile boat: Gun [5], Tac [5] [8].
I also have 2 forever recruits that I pay $20,000/mo salary.
1 has 14560 unspent xp, the other has 6220 unspent xp.
Glitch and the forever recruits uses Centurion with 2x LRM20+++. Effective, and free exp even for unskilled newbies.