THIS CAN BE USED ONLY IN TEST PURPOSE, LIKE WHEN YOU WANT TO CHECK YOUR CUSTOM PARTICLES IN GAME!
Here's video demonstration of that method:
The way it works: In pak01_dir.vpk, in particles folder there's a "particles_manifest.txt" where you can find line about precaching "money_fx.pcf" file, but that file not using in game at all, you cannot even find it anywhere in game files. So if you rename your .pcf file to "money_fx.pcf" it will be precached by CSGO itself. That's it.
Pros of this method: - It easy to do; - You can play mm, while you have "money_fx.pcf" in particles folder; (NOT TESTED)
Cons of this method: - You need to restart CSGO, to update your particles; - You can only use 1 custom .pcf file at a time; - You need to rename your custom .pcf to a specific name; - You still need to use different method of precache (Like sm plugins) to see your custom particles on servers;
Also here's useful link about custom particles: https://gamebanana.com/tuts/11997