Don’t you hate it when people use the same word to describe two completely different things? “Grilling” is an example. It’s cooking things on a grill, obviously, but many say “grilling” when they refer to the process of frying on a griddle which obviously is “griddling”. Grr.
“Pickling” is another instance. In my post “Can I reuse pickle juice?” I took a purist’s approach and specified pickle juice as the liquid that is created through salt fermentation. And no, re-using it is not a good idea because it’s already well inoculated with bacterial beasties which might not get along with a new piece of raw material. Cook with it, drink it, don’t try to reuse it.
But many also refer to “pickling” as the process of preserving a food in a vinegar/salt/sugar medium. That imparts a distinctive taste, but it doesn’t change the chemical composition of the food so I say it’s flavoring, not pickling. Yet, OK, I get it. Instead of making my Quick Pickled Onions from scratch, you could just as easily use the leftover liquid in your Vlasic jar.
I tried this recently with some squishy, uninteresting supermarket onions. The most conservative “pickling” is to dunk your new food in the pickle jar and refrigerate. It will pick up some mild flavor and won’t go bad as quickly so not a bad thing. At the other end of the spectrum, you could bring the pickle juice to a boil and add your foodstuff. I don’t recommend this because it will probably get overcooked.
The middle way is best: heat up the residual pickle juice, then pour it over your food in the pickle jar (having brought everything to the same temperature, or close). That’s what I did with this Pucker’s jar and it’s not bad.