This is a neat mod, thanks for bringing this to the community's attention.
I switched this out myself by going to the f12012/feedback/ (or forcefeedback, on my work comp so can't see the files) directory and modifying the effects.xml file. I found that the file opened in notepad just fine. Even setting the effect value to 0.1 give a nice little bit of rumble in my controller - I found even 0.5 was far too strong for my tastes.
Edit: Got home so I can give the correct file and directory locations:
The file you want is in your F1 2012 directory .../f1 2012/forcefeedback/effectsetup.xml is the file name and path. Make a backup copy of the original file first, just incase!
Open the effectsetup.xml file in notepad and look for the following line of code about half way down the document: <FFBGearChange scale="0.0" gear="-1" freq="35.0" length="0.18" damageScale="1.0" damageLengthScale="0.3" sample="gearChange"/>
You want to change the "0.0" in FFBGearChange scale="0.0" to some value between 0.1 and 1.0. As I said above, I liked just 0.1 with my PS3 controller, but try different settings if you like a stronger feel. At 1.0 you pretty much get the same rumble you would if you shunted the wall at 250kph+.
Props to Blinn to spotting this tweak, it's a nice immersive element in the game.
