I think there is some confusion on this issue. As identified in the thread you posted. You cannot "void" a warranty. You can determine that a failure was not warranted. This means that the failure was not the result of a defect in material and/or workmanship but due to some modification you did to the vehicle.
For instance.....you replace the air filter with a non Ford approved unit and have a Turbo failure due to high vacuum loads and a resulting over speed situation. This was not due to a defect in material or workmanship, but the result of the higher restriction in the non Ford approved filter.
On the other hand, you install an aftermarket air filter and 100 miles later have a cam bearing go bad. This should still be covered under warranty as there is no way the aftermarket air filter could have had any effect on the cam bearing.
Remember, Warranties cannot be void. The failure can be determined to not be the result of defect in material and workmanship.....and that is a different issue that warranty.