Extracting herbs with grape juice
The point of using alcohol to extract things from herbs is that alcohol solubilises things that are not soluble in water. So using grape juice as an alternative is pretty pointless since it is just water with a lot of other water-soluble things in it (like sugars).

So using grape juice is a pretty poor alternative to using alcohol.

Grape juice will ferment under some circumstances, converting some of the sugars into alcohol. But this won't work well unless the conditions are controlled carefully and won't work at all if it is cold (45 F is cold). If you don't do what winemakers do, there is no telling whether it will work or whether it will work without producing nasty results. And pasteurised grape juice won't ferment at all if you don't add yeast and keep it clean. If you don't keep it clean you might well get some nasty strain of natural bug rather than a good wine yeast which will have unpredictable results.

Moreover, the best level of alcohol you are going to get even as an experienced winemaker is 10-15%. This is nothing like as useful as pure or 50% alcohol for solubilising or extracting things that are not water soluble. And grape juice with no alcohol isn't going to be a much better solvent than water (and most likely will be worse as it is already full of other dissolved things).

The old school recipes you are trying to avoid exist because people have tried these experiments before and found what works. Trying to invent new recipes that ignore the "old school" experience is a pretty futile task: what you propose isn't in the old school recipes because it doesn't work.