"With the same guitar as a given, the higher the action, the stronger the torque onto the top. "
Right, in that raising the action height would require a taller saddle, and put the strings further off the top. For a given string height off the top the action will depend on the neck (or fingerboard) pitch, which is pretty much built-in on traditional classical gutiars. There are are a number of makers these days (Brune is one, and I'm another) using various versions of removable necks, which can be re-set relatively easily to correct for improper pitch. Some 'historical copies' use the Stauffer adjustable neck, which gets around the whole issue, and I have seen 'modern' guitars by Stanul and others with removable and adjustable necks.
It's entirely possible to make a guitar that has the correct neck pitch when it leaves the shop, and have that pitch change later. If it changes very quickly that's generally the builder's fault. ALL necks will pull up over the long term, though, no matter how stiff and stable the neck material, simply because the body of the guitar distorts over time. Traditionally this was taken into account by the use of a thick fingerboard, that would allow for some adjustment by planing it thinner at the nut. You get to do this once, or maybe twice, and then the fingerboard needs to be replaced, or wedged up.
Altering the neck pitch itself requires 'slipping the heel' on a guitar that was built on a solera. The back binding is peeled away to about the wide part of the shoulders, the glue joint between the back and the heel and sides is carefully loosened (hope they used hide glue!), and the neck pulled back slightly to adjust it's pitch before the back is re-glued. This is not a repair for the faint of heart: I've never done one myself, and don't look forward to my first one!