Spud, as someone who has screwed with Kali before, and done ****loads of VM testing, trust me when I say you really don't want to mess with a legitimate site, especially if it's hosted on someone elses hardware. Like the mods have mentioned above, there are a ton of legal issues that come with things like Kali, and they MUST BE USED CAREFULLY. Secondly, if you screw up, you can easily wipe out an entire website (If it's got a particularly bad vulnerability). I recommend what the people above me have mentioned, download the sites HTML files, and run it on a Rasperry Pi or a VM if need be. Then go nuts. Avoid actual running sites though.
-Luke