jahenders
Banned
1) Men fought and died to preserve slavery in the 1860's and in very large numbers. No way they are giving it up that quick. That would be saying that their friends fought and died to beat back the "Abolitionist Hordes" just to do the same thing themselves. It would be seen as utter madness. The next generation would seeing at spitting on the grave of their fathers who fought and sometimes died to prevent the abolition of slavery.
2) You would have to change the CSA constitution which would take agreement from planters who controlled the various state governments. Individual states couldn't do as "slave transit rights" in the CSA constitution made it so that if it was legal in even one state it was de-facto legal in all.
3) South Carolina and Texas, at the very least, would threaten to secede from the CSA if even a small step towards abolitionism was made.
I'm not suggesting they'd be happy about it. However, keep in mind their likely trading partners -- primarily the US, UK, and France. It's entirely possible that any of those might impose trade sanctions, high tariffs, etc. on the CSA if they still have slavery by 1875 or so. CSA would feel that pretty quick.
Actually, I think the CSA would more likely start to unravel by around 1875, with some states pulling out and the US being willing to assist them (and take them back) if necessary.