This has been found like a year ago

I don't really understand this "glitch" when you explained it in the video. Can you explain here perhaps?

I'll probably just end up doing it legit anyways

Im not completely sure if it is even a glitch or not; but basically you get either 2 or 3 guns diamond and when you prestige when you use those guns it gives you all the challenges you earned last prestige back within the first 5 kills you get with those guns, if you have two diamond guns you have to prestige twice because the first time you prestige and do this the game will register that you got two more guns diamond when really you just achieved the same challenges you had already obtained. If you have three guns you only need to prestige once and then it will work. Hopefully this helps you all understand more