Anaxagoras
Banned
If I have my time machine, and I'm in charge, Cleburne gets a corps in 1863, and I cross my fingers that he can handle the learning curve in a hurry.
1863 is a bit too early. But there are three reasonable occasions for Cleburne to be given corps command in 1864. Davis could have appointed Cleburne rather than Hood to command the AoT's second corps in February. Cleburne rather than Stewart could be appointed to replace Polk in June. Finally, Cleburne rather than Cheatham could be appointed to take over Hood's corps after the latter was (disastrously) promoted to command the army.
Of the three, the best for the AoT would have been the first. Hardee and Cleburne trusted one another utterly and without hesitation. Johnston got along reasonably well with both of them. So the army commander and his two corps commanders would have been on good terms and willing to trust one another, which is something the AoT never had at any point during the war.
On the other hand, having Hardee and Cleburne in command of the two corps would have been greeted very badly by the remnants of the pro-Bragg faction within the AoT and Cleburne's promotion over the heads of higher-ranking generals would have been taken rather badly.
And, of course, with Wheeler in command of the cavalry the AoT is still effectively blind. Perhaps the best command change the AoT could have done in early 1864 would have been to put the cavalry under the command of General John Wharton rather than ship him out to the Trans-Mississippi.