Now, I'll discuss Jarcho's method. What we're going to do here is that we will clone the existing animation files (.animation, .mesh, and .material files) and make them unique to our custom class. While they are exclusive for our class, they also use the same set of .skeleton files so unlike my method above, you don't have to copy all of the .skeleton files! It's simple yet effective.
1. Just like before, let's create a destination path for your animations, so we need to make a models/pcs folder in your mod folder. Afterwards, create two folders, namely HUM_F and HUM_M.
2. Go to media/models/pcs/hum_f (the original MEDIA folder), and copy the .animation, .material, and .mesh files. Then, paste those three files in the corresponding mod folder. In this case, it's mods/warchief/media/models/pcs/hum_f.
3. Now, rename those three files to your liking. It's important to you name them exactly as the other. In this example, let's all rename them to WARCHIEF_F.
4. Do steps 2 and 3 for the male version. Please take note of the destination paths. You should copy the three files from the original HUM_M folder, and paste them to your HUM_M folder.
5. Again, you can do the following steps through text editing or through GUTS. Let's use GUTS instead since it provides lesser room for error. So, go to Data Editors→Units→Players.
6. Let's first edit the female version, so select the female version of the class, go to Files tab, then change the mesh file that the character is using to the one you renamed. If you have done the previous steps correctly, you should be able to see your mesh on the dropdown menu.
7. Save, restart GUTS, and you now have a “new” set of animations exclusive to your class! Since the custom class will use a unique .animation file, you can now tinker with it any way you want. You can change the particle system that a certain animation is using, increase the animation duration, or anything that your creative heart desires :D But keep in mind that it will still use the base .skeleton files so if those are altered (and saved in the mod's HUM_F and/or HUM_M folder), your class will be affected by the changes. And just like my method above, this method is applicable for custom animations.