Live partitioning was an OS X feature added back in Tiger I think. It has a low degree of risk as long as both partitions are using the Mac OS Extended format, aka HFS+. If you're looking to resize your BootCamp partition after you have already set up Windows, you will need to delete and recreate the partition. This does not mean you have to reinstall Windows and the drivers again, Winclone allows you to backup your Windows partition to an image and then write the image back to the larger partition once you've recreated it using Boot Camp Assistant.