I don't know if someone did that, but here is what i've just done with my UMP45 class.
Having 2 attachment without the proficiency and having a proficiency not available for my gun.
(Grip don't work on most weapon who don't have it by default)
Also, having Assault's killstreak with Support killstreaks system (continue if you die)
And it works. I tested it out !
If you want me to explain what I modified just ask.
Download link of my first version at the bottom of this post.
(Actually you can only modify the 3rd Class)
Virusscan for the .rar : https://www.virustotal.com/file/dccf...is/1336660364/
/!\ THINGS YOU MAY KNOW /!\
1. Assault rifle + Grip => Invisible Gun Bug.
2. Assault rifle + Rapid Fire => Invisible Gun Bug after like 2-3 Games.
Feel free to share what you tested, I'll add it to the list.
Special Thank to Jorndel for a part of code I used.