Wirelessly posted (HTC Diamond: Mozilla/4.0 (compatible; MSIE 6.0; Windows CE; IEMobile 7.11) Sprint MP6950SP)
Maybe you could use an app like sktools that could search for and allow you to clear the data you want to clear out?

Also, I would think if you altered the correct data on your pc slightly (which would have a newer timestamp than the data on your device) when you sync the data on your device should be updated.