There's actually a relatively easy PoD which can more than
double the CSA's heavy industrial capacity. It requires going back about 8-10 years before the ACW, but it's not the sort of change which would automatically butterfly away the ACW by doing so.
The CSA's biggest industrial problem in OTL, apart from the the blockade itself, was a perennial shortage of raw iron ore production. The most famous CSA industrial works, the Tredegar Iron Works, underwent a massive expansion during the ACW, with a much improved capacity for manufacturing steel and for making all sorts of things from steel. The CSA also made a very large expansion of ironworking at Selma, Alabama, which became their second-most valuable manufacturing site. (Particularly after the Cumberland Iron Works in Tennessee were captured).
The problem was that neither Tredegar nor Selma ever really operated at more than half of their capacity. The CSA was capable of building factories and finding skilled workers - that was not the problem. The problem was a shortage of raw iron ore; Tredegar got less than half of what it needed for most of the ACW. No number of skilled workers can help if they don't have the right raw materials to work with. The Rebs simply didn't have enough raw iron ore production anywhere, and that's not the sort of thing which can be built up overnight. Thanks to the blockade, they had no way of importing it either.
The reason for the South's lack of raw iron ore (pre-ACW) was not what might be thought, either. It had nothing to do with any CSA sense of being anti-industry (the idea that the South was anti-industry is much-overstated). What happened was that due to an unfortunate (from their point of view) confluence of timing, the CSA was pushing for independence at a time when their iron ore production was being quashed due to internal competition.
What happened in the USA (North and South) up until about the mid- to late 1840s was that most iron ore production was local, relatively small-scale, scattered across many sites in many states (New England, Upper South, Lower South, etc). All of this used charcoal for iron smelting. But then along came Pittsburgh, the use of anthracite coal, and blast furnaces. That was a more efficient process than the ones which went before it, and Pittsburgh iron put many of the local iron producers out of business... in both Northern and Southern states. In Virginia, for instance, iron production
decreased between 1850 and 1860, at a time when the rest of its manufacturing was expanding. This was not just a Southern thing - New England iron ore production collapsed, too. Pittsburgh and a few neighbouring anthracite-using states took over most of the USA's iron production.
So where in 1840 or even 1850 you had a lot of small-scale iron producers in most states (North and South), by 1860 many of those were gone or in severe decline. And then, right at this confluence of timing, the ACW breaks out - and the CSA is starved of raw iron production, right when it needs it most.
So, how to change that? The answer is something I touched on in an old thread
here. Getting the Birmingham, Alabama site up and running a couple of decades earlier.
Around 1850, there was a syndicate of rich planters and industrialists in Alabama who wanted to develop the Birmingham site. (Yes, pro-industrialisation planters and slaveowners did exist). They knew that the iron ore and other resources were there. What was needed was a relatively short extension of a couple of railroads to cross there, so that transportation could be decent. But the proposal was killed by small farmer opposition in the Alabama legislature, which more or less put things off for a decade. Then when a similar syndicate wanted to try again in the late 1850s, the buildup to the ACW killed the idea again. What with the ACW and all, Birmingham was not opened until 1871.
If the syndicate had been successful around 1850, by 1860 Birmingham would have been a major source of iron ore production, and sitting on the necessary railroads to bring it to where it was needed in Selma and/or Tredegar. (Or it might turn out to be better just to expand things in Birmingham, but either works). Presto, a CSA with more than double its manufacturing potential. Still vastly outweighed by the North, but the difference is not nearly as bad as it was in OTL...