Modify Starting Cash
You can edit the dark.cfg file and add the line "cash_bonus n" N
represents the amount of cash added to the beginning of a mission.

Skip to Next Mission
Press [CTRL] + [ALT] + [SHIFT] + [END] to skip to the next mission.

Increase Cash (Bug Exploitation)
Just before completing the mission, do a save or quicksave.
Complete the mission and save it in a different save slot. Reload your
last save or quicksave before completing the mission. Complete the
mission again. The statistics screen should now have ADDED TOGETHER
the loot from BOTH mission completions. Apparently, the variable which
stores treasure amount at the end of the mission is not being cleared
between loads. You can keep doing this until you have all the cash you
need to buy out the store at the loadout screen for the mission
immediately following.

No Killing Rule
This involves editing the USER.cfg file, first make a copy of the
file, then add the following lines "cheats_active", "nokillgoalcheat"
this will alow you to win with out worrying about the no killing rule
in some missions.