BZPower never on an invision free template as it was never hosted on invisonfree. There was a period where it was on a default skin due to upgrading the forum software and the old skin becoming incompatible. As for the current skin, it was modernized take on the original skin. It could probably be updated with some new tricks at some point, but it'll likely remain largely the same. And if you want the default invison skin, you could always just switch to it.