There are two types of Alternate Attires known in WWE 2k games. The first type are Alternate Attires created via the game's Creation Suite, which are basically CAWs. The second type includes the existing Alternate Attires some default wrestlers in the game have as well as modded alternate attires. The two are completely different formats.
Type 1: CAW Alternate Attires
These alternate attires can only be created via the in-game Creation suite or downloaded from in-game Community Creations. They are basically CAWs and are saved and encrypted inside your save game when you save your game. They aren't affected by the Universal Alternate Attire Unlock and of little relevance to modding.
Type 2: Default Alternate Attires and Attire Mods
These attires typically come in the form of chXXXYZ.pac file for each attire. They can be treated like regular Wrestler Mods. Please refer to Installing Mods to find out about how to install them. To access these Attires in the game, you'll have to use the [] that is part of Data Editor.