100% ingame. There's no practical way to mod Halo: Reach, and I wouldn't if I could. I do use Photoshop to do other effects and add things that aren't there.
Updated to Page 7 of Chapter 4.
Phoenix Seven has it's own forum category over at HaloSprites forums, where the bulk of the material is placed. I'll still keep this page updated, but it won't be as robust.