My understanding -- and I could very well be wrong on this -- is that Texas has the right to divide itself into 10 (?) separate states.
But that's something I've only heard, never read. Hopefully, somebody here is better able to answer the question. I'm curious about the answer myself.
That may have been true pre 1865, but texas was required to re-write its Constitution post Civil War. Texas does not have any right to split itself, absent consent of Congress.