The decals are just four 256x256 .vtfs (which I welcome you to change!)
and 4 .vmts (which you can change too! Sparingly!)


Essentially, treat these like 4 sprays - one for each team.
Just like Sprays, they can be fading / distraction decals, or animated ones!
Even a step further, since you can modify the framerate of an animated decal via the .vmt!

Hopefully, this should make things easier to access!

If you want an easy site to convert images to .vtf, try this one! "VTF Spray Converter for TF2";
https://rafradek.github.io/Mishcatt/