You mean change their expressions? Like smiling, frowning, etc? Yikes. That's a bit complicated to explain.

Unless you meant re-skinning the faces? Changing the way they look? That's a bit easier.

Oh, that problem. Now I see what you're getting at.

It has to do with lighting. The lighting system in Tron 2.0 is . . . a bit strange.

You need to use directional lights (DirLights) in your maps, to get certain models to be lit properly. In fact, you could light your map with just DirLights. I prefer to use both types (regular and DirLight). It seems to give slightly better results. But using just regular lights alone, causes the effect you're talking about.

For now, you can just create one DirLight, which behaves like a spotlight. What you want to do is move the DirLight far away enough from the map and widen the beam enough so it covers the entire map. You'll need to increase the brightness so it lights such a large area, well enough. Eventually you'll probably want to use more than one DirLight, to cover the map from different angles. Monolith typically used at least three DirLights on every map.

You can put DirLights outside of your skybox, if you're using one. The Lithtech engine is unusual in another way too, by allowing objects outside. Just about every other game engine throws a fit when you put objects outside the skybox.

Yeah, you really should be using a skybox.

With the DirLights . . . keep at it. You'll get it eventually. You need to play around a lot with the positioning and properties.

Load the sample Disc Arena map that came with the tools, and study how Monolith used the DirLights in that map. Try to copy what they did.

I wasn't using a SkyBox because I was aiming towards using this particular world as a prefab. And I'm not sure I will release this. It's not good enough to be released (yet, at least).
I'll try using a skybox. Thank you TronFAQ, you're always a big help!

Hmm, well let's go through it step by step.

So you've made your brush box. You resize it so it's big enough to enclose the entire map. Then you need to flip the faces by pressing the F key on the keyboard. After that, you check its Properties and set its Type to SkyPortal. And then you change Detail to False.

Finally, you click on the Prefabs tab on the left and navigate to Prefabs\M01\Skybox, then double click on the SKY01C icon. The sky prefab will appear in your map. Place it somewhere outside the skybox, either above or below.

That's it. The sky should appear now. The documentation that comes with the tools makes it out to be a lot harder than it really is.

OK, I tried that. Nothing changed, except that now I have a Skybox. But nothing changed on my person's face.

On a side note, why don't the Prefabs work? I use the "Import World" function, and it works fine, but it might be easier to have a Prefab directory.

YAY!!!!!!!!!!!!!!
Thank you TronFAQ!
I used the FastLightObjects=False and turned up the ObjectBrightScale, and I got the character's face to light up!