Enxur it doesn't seem to do anything.

To apply to Gordon: Add override materials to the model, add attribute in element viewer for gordons head add it as a "String" attribute. Then click the + on his head model and click on the side panel next to string and type or copy and paste: models\red menace\HLA\Gordon\gordon_head_color_damaged.vtf

How do I apply it to him?

This would probably work best for Post-Cascade or Post-Citadel Collapsing animations.