Uhhh, well, if you want to fuck VAC that badly...
First, recon. Find out what hardware and system software the Valve network uses, and find some holes and exploitable weaknesses in it.
All of the following will need to be done on a ~1.5hr, 2hr max timeline.
We'll need around 150-180 computers to pull a DDOS on the VAC server database and any backups, so basically the whole network. In fact, nuking the entire Valve network might even be a good idea(well, none of it is a 'good' idea, but you get what I'm saying).
Presuming Valve keeps their security systems on the same network(likely), enough packets overflowing the network will bring the whole thing offline at least, if it doesn't crash it outright. If it doesn't crash the network entirely, use an exploit to start crashing or gaining access, whichever proves more effective.
During this time, Valve will doubtless be working to reboot their servers. While this is occurring, several crackers have scarce moments to enter the system (presuming they can get in) before the main security comes back online.
Once in, erase the cheat DB and the ban DB. Do the same to all backups, wipe any logs left, and leave. Don't touch the Steam servers, financial stuff, etc., just VAC. This way if anyone gets prosecuted it will only be for software damages, not theft.
They'll have to re-detect every single new cheat, and re-ban every hacker.
It will be like a goddamn jail break.
(This is all pseudo...I've never tried to pull off anything this large
)