The magic word here, IIRC, is "Manumission", a slow, step-by-step emancipation. Brazil OTL IIRC set a "born after" date where all children born from that day forward are automatically free, though an "all free by date X" is a possibility too. You will see a lifting of any bans on slaves renting out their services to buy their own (or family's) freedom, which was common with the many skilled slave craftsmen/artisans.
Sam H hit the nail on the head here. A slow, iterative process that will see many of the more diehard plantation people move south, possibly to NC or TN potentially swaying those states further into the Deep South sphere. Possibly just into the Deep South. I'd assume MD and KY follow suit on manumission, TN too, potentially also MO and AK. NC depends on any demographic shifts due to VA expatriation. Freemen will, as OTL, find a hard time in VA and MD as a threat to "proper white people's jobs" and will likely be strongly persuaded to find a new place to live. One option is West, leading to a larger black frontier population (they won't find much welcome in the Midwest). Black Kansas?!? Another option is Liberia, and there were OTL rumors among the Freemen population that Libera was a "promised land".
A larger Colonization Society means more Freemen to Libera; not a gigantic number due to the costs, but potentially enough to maintain a larger American-Liberian population that's more than just an aristocratic class...potentially more integration with native populations. Interesting butterfly potential there.
VA will as others have stated go more industrial than OTL. "WV" has huge coal deposits to drive just such a revolution. Mills will happily open up that much closer to the cottonfields. *Roanoke (called Big Lick at the time, though Salem may become the Big City ATL) will become a transportation hub a lot sooner. The new jobs mean similar demographic changes as we saw in NY, PA, MA, etc. with more immigrants to fill the jobs. UNLESS...these dangerous new jobs simply become the perfect place for Freemen to be put to work away from "white people's" jobs.
TX is a real foggy area. There's still a "Manifest Destiny" mindset growing in the US to justify expansion. Unless Oregon comes along to satisfy this TX-CA still looks very inviting. There're also strategic concerns at play: TX is a damned good place to stage an invasion to seize New Orleans, at least in theory (swamps and all). Galveston Harbor alone is a good place for any hostile naval presence. Jacksonians will likely want to seize TX just for the sake of seizing TX! There's also the question of how much hostility to slavery there is in the US. I really don't see VA or any other of the "midatlantic sphere" becoming any sort of major place for anti-slavery or even anti-expansion (that was much more a Midwestern "Freesoiler" thing). The "antislavery" movement in VA was mostly economic, plantation owners like Washington seeing the "peculiar institution" as a financial burden to the Master as much as to the slaves. There likely will be a laizes faire view of slavery. "We cast off that lot a while ago...if some states want to bear that burden they're welcome to it." Much depends on other unpredictable butterflies IMO, but it's perfectly logical to assume an OTL-like situation happens over TX. The thorny issue is how many states do you make of it? The Deep South will want as many as possible, but they wont have the votes in the Senate to push any major compromises along those lines. There *could* be an earlier secession crisis ATL.
One other interesting butterfly is that the Deep South slave population is even bigger. This means slave costs are down and the demand for slave import is lower. It also means fears of a Haiti-style uprising grow proportionately with the black-white population balance. I can see the Deep South becoming truly paranoid about their Black Powderkeg with...frightening possibilities.