Following on from The Universe Is Slightly Different, we reach the end of Flashpoint and the start of the reboot-in-some-places-renumbering-in-others-try-not-to-think-about-it DC Universe.
One thing I didn't discuss last time was reasons why the universe is reshuffled. Obviously it has to be some pivotal event right at the start of the change, or several events changed deliberately, to have such wide-ranging effects.
i.e. not really what Flashpoint did.
So yes, come up with a solid reason which makes sense, even in a Butterfly Effect kind of way. A central change or changes where the connections hang together logically. If this reader's first reaction is "but that makes no sense!" then it's not a good sign.
Oh well, it did lead to some amusingly wonky not-very-parallel alternative scenarios like "Alaska, Land Of The Undead".