Instructions
Preparation/Extracting Your Desired File to Modify
Download the following programs:
GCFScape or GCFExplorer
.vtf plugin for Photoshop
(See Resources below).
Follow the instructions with the .vtf plugin download to install it into Photoshop. The instructions are indicated in the "Readme" file.
Ensure that your Steam, and any programs running through Steam are closed.
Prepare a folder for the purpose of backing up any textures you wish to modify. This procedure does not necessarily require backups, but it is a good practice to back up any textures you wish to modify; it's a pain to retrieve a default texture a second time.
Open your chosen GCF browser software, and open your TF2 .gcf file in said program. It is typically located at "C:\Program Files\Steam\SteamApps."
Inside the .gcf file, go to "tf\materials\models." From this location, if you wish to modify a character skin, go into "player." If you wish to modify a weapon skin, go into "weapons>v_models."
Extract your .vtf of choice to your folder for backup files, and create a duplicate. Be absolutely sure you do not modify at least one of the two identical files of each texture.
Editing Your Desired File
Open Photoshop with .vtf plugin installed. Use the software to open whatever .vtf file you desire to edit.
Edit the desired section of texture into a desired custom skin -- bacon patterned pants, for example. Creativity is highly encouraged. Be very sure your effects are kept within the desired section of your texture. Failure to do so will cause your custom texture to overlap in undesired areas and ruin your skin.
Save your modified texture over your old texture, making sure you have your backup prepared. Do not modify the extension; your file must be .vtf. A dialog will appear when you attempt to save, asking for .vtf options. Do not modify any of the options; leave them AS-IS in order to have a ready-to-use .vtf skin file.
Applying Your Skin
Create the following folders at the following locations, the quotes indicating the necessary name:
~\Desktop\"materials," then ~\Desktop\materials\"models"
The following directories must be created at this point:
~\Desktop\materials\models\"weapons" (or "player," depending on whether you modified a character skin, or a weapon skin).
If you modified a character skin, create a folder within the "player" folder with the name of the skin's class that you modified (i.e "medic," to remain in continuity with the tutorial. Note that all the characters are lowercase.). Place your modified player skin within the class-named folder.
If you modified a weapon skin, create a folder within the "weapons" folder named "v_models," and place your skin file within.
Once you have made all of the above directories, and properly placed your file(s), take your created "materials" folder and place it within the following directory:
"C:\Program Files\Steam\SteamApps[yoursteamusername]\team fortress 2\tf"
To ensure the correctness of your efforts so far, check to see that the directory you have created is similar to the pictured directory in Reference 6 below. If so, you have successfully created and applied a skin to your tf2 models.