Since you apparently didn't read when I already addressed this in advance, I'll repeat it again.
While the CSA 1.9 prohibits the General government legislating against slavery, CSA Article 1.10 does not mention slavery in any regard. It’s entirely committed to ex post facto and other non-slavery related issues, e.g., excessive bail, entering treaties, laying duties on tonnage and so forth.
,b>So proponents claiming CSA Article 1.9 stops the States from becoming Free States is incorrect. It is solely a prohibition against the General government. If the CSA Founders meant to stop the States from becoming Free States, they would have had to provide that prohibition in Article 1.10.
The Confederacy’s addition to 1.9 denying power to the General government to disestablish the institution of slavery was done so the prohibition would be explicit. Slavery was already implicitly outside the General government’s power when the CSA Founders abolished ‘dual sovereignty’. Slavery, as with any State creation, resided in the sovereignty of their respective peoples.
So not only was there nothing in the Confederate Constitution which would have prevented any Confederate state from abolishing slavery, there was also nothing in the Confederate Constitution which would prevent any state that had already abolished slavery from joining the Confederacy.
". . . delegates from the Deep South met in Montgomery, Alabama, on February 4 [1861] to establish the Confederate States of America. The convention acted as a provisional government while at the same time drafting a permanent constitution. . . . Voted down were proposals to reopen the Atlantic slave trade . . . and to prohibit the admission of free states to the new Confederacy. . . .
"The resulting constitution was surprisingly similar to that of the United States. Most of the differences merely spelled out traditional southern interpretations of the federal charter. . . .
". . . it was clear from the actions of the Montgomery convention that the goal of the new converts to secessionism was not to establish a slaveholders' reactionary utopia. What they really wanted was to recreate the Union as it had been before the rise of the new Republican Party, and they opted for secession only when it seemed clear that separation was the only way to achieve their aim. The decision to allow free states to join the Confederacy reflected a hope that much of the old Union could be reconstituted under southern direction.". (Robert A. Divine, T. H. Bren, George Fredrickson, and R. Hal Williams, America Past and Present, Fifth Edition, New York: Longman, 1998, pp. 444-445, emphasis added)
ARTICLE IV
Sec. 3.
(3)
“In all such territory the institution of negro slavery, as it now exists in the Confederate States, shall be recognized and protected be Congress and by the Territorial government; and the inhabitants of the several Confederate States and Territories shall have the right to take to such Territory any slaves lawfully held by them in any of the States or Territories of the Confederate States. “