Textures.ini

"materials/old/wood_crate.vtf" "materials/custom/hd_wood_crate.vtf"

Let me know, and I can give you a much more precise answer. textures.ini

Now go forth, open Notepad, and start redirecting. Your game world will never look the same. "materials/old/wood_crate

: The current required version for PPSSPP texture replacement. hash = quick textures.ini

; Texture Overrides for My Custom Map "brick/red_001" "custom_bricks/red_001_hd" "metal/rusty_door" "metal/door_shiny" ; forces a shiny door instead of rusty

At its core, is not a texture file itself (like a VTF or TGA). It is an Initialization file that tells the Source Engine (and similar GoldSource-era derivatives) how to handle specific textures in memory.