Thanks for the code, but in the newer versions of boinc, isn't there an option for this in the advanced menu?
You can disable the GPU by selecting Suspend GPU from the menu. But, it will still register that your GPU is capable and ready, so although in theory this works, if you really want to be safe from doing those WU like Ford, best to edit the config file.
Personally, I'm going to dump F@H at the end of the month so that I'm ready, willing and able to take beta wu's. Hopefully the opt-in option will be announced so I don't have to check the site every couple of days.
You need to opt-in to BETA testing as it's not enabled by default. Log on to your WCG page, select Beta Testing from the left hand side, then choose what profiles you want the WU to go to. Just be aware that it is for testing WU from all projects, so there is a chance of finding bad WU's. They're also very rare normally, it is the most difficult Bronze/Silver to earn so even with it enabled don't expect the usual numbers of WU you normally get in WCG.
If the BETA is succesful it's likely that the default setting for HCC will be to enable GPU WU if there's compatible hardware and BOINC preferences are set to allow.
That's as much as I know, from what WCG admins have shared so that should hopefully help those who don't want to join to go trouble free and those who do want to join, know where to look.
Personally I participate in Beta testing as I'm all for helping the IBM staff to get stable and well-tested WU before they go live. Whether I join HCC GPU once it's out.. don't know yet. Will wait till the testing is over and the researchers announce what level of accuracy they achieved.