Numbers are from the 2008 Edition:
5.24.4.1 Requires that welds ground flush may not reduce the thickness of the thinner base metal by more than 1/32" or 5%, whichever is less.
5.62 explicitly allows grinding in the use of repairs, but it does prohibit nicking or gouging the base metal.
The visual inspection required in 6.9 is generally understood to be performed before grinding flush, caulking, machining, or any other code-allowed finishing of the weld. This would not preclude repairs by grinding, such as removing excess reinforcement or overlap.
Other than that, I believe grinding is allowed unless addressed specifically in the contract documents.