The Conqueror's Collection Cheats

You must first complete "Rescue the Mutants". Get the Ghost Stalker and the Mutant Hijacker, they must be present when you complete that mission.

Then, as you play "Destroy the Chemical Plant", build your base and attack Nod. Take a small number of troops to the upper left corner of the map for a little surprise...

You will hit a train station. And, a Ghost Stalker will arrive as a reinforcement trooper. He MUST be kept alive. Board the train and while you are at it, destroy the remaining Nod Base. You will hit the unlocked "Mine the Power Grid" mission.