It won't hurt to try it but I honestly doubt it will have much effect as it is a preventative, a pre-processing treatment and any softening will have already developed.

Dave

Dave is 100% right on. If you forgot to add it when processing, don't bother later on. It will not ever "firm up" anything that has "gone soft".
Jim in So Calif

On a slightly related note, would pickle crisp be effective for refrigerator pickles that are not being processed at all (but still as a preventative), or is the processing important?

Csiga,
Pickle Crisp, or generic, is usually used by me in refrigerator pickles.
Even with fermented pickles, I add generic Pickle Crisp after the fermentation period is completed at room temperature, and just before placing in the refrigerator, just as Dave suggests.
Works great.
Jim in So Calif

Where do you find generic Pickle Crisp? I've not heard of it. I'd love to find a cheaper generic version.

Where do you find generic Pickle Crisp?

A search here will pull up many discussions about it and sources for it. bulkfoods.com is a common source as is canningpantry.com

Dave

Thank you ... i tried the grape leaves last year and I'm not sure they were quite successful :) I wanted to try pickle crisp this year ut my first batch is refrigerator pickles and I just wanted to make sure ... thanks!