You seem to be putting a bandaid on an underlying problem. A really bad bandaid, at that.
If your RAM is causing errors, then it's time to RMA it. Kingston RAM has a lifetime warrenty, so why not get the most out of that.
Even if, magically, you were able to underclock your RAM that far, it would seriously cause problems with system performance. It's supposed to be running at DDR400, and you want to bring it down to DDR166? That's more than halving your memory bandwidth.