At the end of the theives guild do you cause a Dragon BREAK!?!? or not?

Scratch that.

I believe so. Notice how documentation on the Thieve's Guild cannot found (as stated http://www.imperial-library.info/obbooks/myth_menace.shtml), but can easily be referenced http://www.imperial-library.info/obbooks/thief_virtue.shtml.

Marius Caro very plainly states that history has been changed, and now they have guildhalls.

No, breaking the dragon typically involves a new god taking its place in the pantheon, which makes Akatosh get very confused, or according to some even makes Akatosh step aside for a while.

What happened in the Thieves Guild was simply a rewriting of history. (Funny how no one actually explained how that worked, because one you'd think that if all you needed to do to alter history is grab a scroll and mutter some words, the Empire would constantly be rewriting the world. Of course it could be, because there's no way we'd notice but that's not cool.) All the elder scrolls seems to have done is undo the conceiling effects of the Cowl of Nocturnal.

So in truth the only thing the elder scrolls did was allow us to see things that were already there but that were hidden from our sight.

Well, wouldn't something like the rewriting of history itself constitut a literal break in time??

It's Nocturnal's Cowl, not Akatosh's.

Things are hidden by shadows or memories are stifled by darkness. Something appears so chaotic and formless that the it doesn't register. All useful anologies.

So it was more of undoing the effects of the cowl, so that people can see and remember what was hidden, not even changing history, but revealing it? Deadric Princes must be pretty powerful

More like a dragon hiccup.

No, Corvus Umbranox said that history has been changed. Marius Caro is the count of Leyawiin.