Sadly, making up commands doesn't work, you can only use the ones in the comref. ;D
You can't change the opinion of the Restance in the middle of a game. You can fake it by using setCaptive commands, the trick C0LDSt33L mentioned, or deleting units and replacing them with others when the player isn't looking. Alternatively make a mini-campaign, which looks like one mission but is in fact two, with the Resistance on different settings in each.