When I was clerking at the Indiana Judicial Center we law clerks had a discussion about these things. We called them “Prospective Repealers” and the consensus was that they could not be binding on a future legislature. However, in this case, if you read the first section of Article VII, as slavery being a “fundamental right” before all others, the Kansas Supreme Court could hold that slavery is a “fundamental natural law” that cannot be abridged, including by Constitutional Amendment. The inclusion of Section 14 of the Adopting Schedule was a reaffirmation of that.
These provisions were not unknown in the Constitutions of southern states generally. For my “We The People” team last year, I reviewed a number of those prewar Constitutions, and most of the slave states had similar provisions. When it came down to “state’s rights” as the basis for secession, it appears that in most of these states the only right they really cared about was the “right” to own other human beings as property. And they really didn’t intend to let it go.
These provisions in the Lecompton Constitution show that the slaveowning politicians in Kansas saw their state as being 100% southern in all aspects of its organization and operation.
"Their main purpose, as indicated by all their acts of hostility to slavery, is its final and total abolition. His party declare it; their acts prove it. He has declared it; I accept his declaration. The battle of the irrepressible conflict has hitherto been fought on his side alone. We demand service in this war. Surely no one will deny that the election of Lincoln is the indorsement of the policy of those who elected him, and an indorsement of his own opinions. The opinions of those who elected him are to be found in their solemn acts under oath - in their State governments, indorsed by their constituents. To them I have already referred. They are also to be found in the votes of his supporters in Congress - also indorsed by the party, by their return. Their opinions are to be found in the speeches of Seward, and Sumner, and Lovejoy, and their associates and confederates in the two Houses of Congress. Since the promotion of Mr. Lincoln's party, all of them speak with one voice, and speak trumpet-tongued their fixed purpose to outlaw four thousand millions of our property in the Territories, and to put it under the ban of the empire in the States where it exists. They declare their purpose to war against slavery until there shall not be a slave in America, and until the African is elevated to a social and political equality with the white man. Lincoln indorses them and their principles, and in his own speeches declares the conflict irrepressible and enduring, until slavery is everywhere abolished."
Robert Toombs speech to the Georgia Legislature, November 13, 1860, advocating secession.
No, there is no doubt what "right" Toombs and Georgia were willing to fight for.