I think the President and Congress have to approve it too
I think only congress has to approve it.
The fact that they wrote in this waiver for Texas (which still stands today for Texas to possibly break-up)....has never been challenged in court as to why one state gets that waiver, and none of the other forty-nine will be given that chance.
Under the right circumstance....I could see a challenge, and some Supreme Court judges grinning because they get to go back 1850s law, and debate a screwed-up waiver that got thrown into the mix and accepted for over a century.
Would the Senate even want to debate this? McCain, I would imagine would laugh and say “no-way”. Same for most of the Democratic leadership. The Supremes might not laugh that much and say that the Texas waiver opens the door for this split.