How does one go about doing that? I've never done any editing with this game before.
Go to your game folder. There you will have subfolder Battlesets with NWAC in it. Look for file Scenario_c01s12.nwscenarios . Copy it somewhere safe as a backup.
Open the original file with the text editor (notepad is enough).
Look for Landing Force North and then PositionInfo. Just below are coordinates. Edit them to your will.
Repeat this looking for Landing Force South and then PositionInfo.
Save. Enjoy.