If you've ever tried to make a Minecraft video, you've probably run into the numerous problems of costuming ingame. The skin server can take forever to update and you have to reboot your client just to check, and usernames are always getting snapped up while you wait a month to change one on yet another purchased account.
Not anymore.
Features
With the Wardrobe Mod, you can configure a vast array of different costumes, each with different (or identical!) usernames and skins. You can give them Alex's small arms, you can have them only change your username or only change your skin, and you can even adjust or disable the particle effect of changing costume to really nail down the look you want.
This mod also comes in two versions, one client-side only which can be used on any 1.8 server and one server-side to help everyone know what's going on in your filming sessions.
Instructions
First things first, go into your config file and find the wardrobemoda or wardrobemodb file (depending on whether you're using the Client or Server version, respectively).
Under Costumes, you build up your collection. Each costume has a reference name, a username, and three booleans controlling whether it has small arms, changes your username, and changes your skin.
Then, you need to include the skins for the costumes in your texture pack. Inside the assets folder of your resource pack, add a new folder named either wardrobemoda or wardrobemodb (same as the config file) and give it a skins folder too. Inside the skins folder, dump all of the skins for your costumes. Remember that each skin file must be named in correspondence with the reference name of the costume used in the config file. If the costume is set to not change your skin, you don't need a skin for it in your resource pack. Also remember that everyone playing on the same server with the Server version of the mod will need the same skins to see the same thing.
With that done, your wardrobe is now ready to go. Hop ingame and type /wardrobe list to see all the available costumes in the wardrobe. To alter your particle settings, type /wardrobe particles <true/false> to turn them on/off and /wardrobe particles <particle name> to change what kind of particle is displayed when a costume is changed. Lastly, use /wardrobe set <costume reference name> <optional target or all> to apply costumes to yourself or others, and similarly /wardrobe clear <optional target or all> to remove them.
That's all there is to it! Enjoy