There is nothing in the Texas constitution allowing internal partition.
Where is the legal documentation reflecting the provision you refer?
Thanks.
It was in the US annexation of Texas, IIRC, that Texas had the authority to divide itself into as many as 5 states.
Texas annexation was by Joint Resolution of Congress, and put to a vote, and agreed to by the electorate of Texas.
The Joint Resolution of Congress has the provision permitting Texas to divide itself.
On the other hand, Texas claimed more land, and some of the land they claimed has been divided into parts of what are now New Mexico, Colorado, Kansas, and Wyoming.
So it would be an interesting court case, and I don’t know how it would end. Of further interest it may be the kind of controversy that would, per Article 3 of the Constitution, have the SCOTUS as original juridiction.