Recanning can cause problems, including bacteria getting in. I posted a similar question about canned mushrooms in big 10 pound metal cans, and wanted to repack in pint jars. They cannot be done. If you recan in smaller size jars, they do need a BWB to process to properly can them. If you do that step, the relish can get quite mushy. Because its a relish, I would expect that any watermelon would be finely chopped, and only the white part and skin would be used. It might be better fill smaller jars and refrigerate, as opposed to a reprocessing with heat. Another option is to try and duplicate the relish yourself, and see if the results are similar to store bought as to texture and taste. I made a relish two years ago that used finely chopped cukes, onions, vinegar, and spices. After making a batch, I also made mustard pickles. I thought the two in combination would be great on hotdogs. They are really tasty and much more flavorful compared to any store bought.

I would not hesitate putting up in smaller jars and following the processing times for home made relish. I would certainly heat it first. If it came in a plastic gallon container, you can be sure it wasn't HWBed. There probably are many preservatives in it anyway. Just my opinion.

if you're going to heat it and process it, the texture will certainly be changed. Why not try freezing a sample? Sweettalk the restauranteur and get a small amount, freeze it for a few days and see if you like the texture. It sure would be a lot less work, -- kay

I would not can this. You have no idea if it is designed for canning. There are cooking recipes and safe canning recipes.
You need to use this fresh for safety reasons.
We never recommend recanning large commercial products.

I think I knew that it wouldn't do the relish any good to re-can it in smaller jars. But I thought I would come here and ask the experts.

After I open a jar, I'll just share it with the family members that like it and tell them to keep it chilled for no more than 6 months.

Thanks to all that replied.

I would not re-can a commercial product but, Teresa's relish would be the exception. If there is a safety issue re-canning it, I would not. I'll agree the quality may be compromised. I won't use store bought tomato sauce in home canned salsa as is listed in some approved recipes for canning. I use fresh homemade sauce.