Can you switch from the standard factory halogen headlight to the factory xenon hid headlight on the 2011 Buick regal, I saw a pair for sale on eBay with the ballast included

I'm not sure whether or not it would work, but if I may suggest, stay away from the cheap Ebay HID kits. They are known for bad ballast that cause electrical noise, and they fail sooner than normal. As the old saying goes, "You get what you pay for".