I may be off but that is what is sitting in the back of my mind.
No - Texas JOINED as a republic but then seceded. After the war we had to come back under the damned yankees conditions.
Your are correct. Texas can leave the Union anytime it pleases and needs no permission from the FedGov
That was under the original Texas Constitution.
Q: Doesn't the Texas Constitution reserve the right of Texas to secede?
A: This heavily popularized bit of Texas folklore finds no corroboration where it counts: No such provision is found in the current Texas Constitution[1] (adopted in 1876) or the terms of annexation.[2] However, it does state (in Article 1, Section 1) that "Texas is a free and independent State, subject only to the Constitution of the United States..." (note that it does not state "...subject to the President of the United States..." or "...subject to the Congress of the United States..." or "...subject to the collective will of one or more of the other States...")
Neither the Texas Constitution, nor the Constitution of the United States, explicitly or implicitly disallows the secession of Texas (or any other "free and independent State") from the United States. Joining the "Union" was ever and always voluntary, rendering voluntary withdrawal an equally lawful and viable option (regardless of what any self-appointed academic, media, or government "experts"—including Abraham Lincoln himself—may have ever said).
Both the original (1836) and the current (1876) Texas Constitutions also state that "All political power is inherent in the people ... they have at all times the inalienable right to alter their government in such manner as they might think proper."
Likewise, each of the united States is "united" with the others explicitly on the principle that "governments derive their just powers from the consent of the governed" and "whenever any form of government becomes destructive to these ends [i.e., protecting life, liberty, and property], it is the right of the people to alter or to abolish it, and to institute new government" and "when a long train of abuses and usurpations...evinces a design to reduce them under absolute despotism, it is their right, it is their duty, to throw off such government, and to provide new guards for their future security." [3]