Doesn't work that way.
If you switch to 1024 res and it builds the cache, you will see individual folders with *****_1024.cga filenames. The 1024 denotes the resolution of that cache file. If you have built the cache for 512 previously, you will see the same filenames ending in _512.gca (or whatever the extension is, I can't remember here at work).
If AH can run the resolution itself, it will load hi-res in that resolution.
The way to find out is to load a skin and look at it closely. Look at the cockpit, the wing outside your cockpit, zoom in on the runway and look at the details/noseart.
Then switch back to 512 resolution, and do the same. You'll notice a slight loss of detail (things just a hint less crisp).