Parser functions cannot change your skin because they're used with the content area. You can change your skin with Special:Preferences or for a quick change use SkinSwitchButton. You can probably build something a little more permanent if you really want, but this suits most of my needs.
Well the only real differences are the page width and the existence of the Mainpage 'sidebar' advert. Assuming you're using the main page column tags, and set the widths to 100% you shouldn't have an issue.