Depending on the amount added - 1 cup is a substantial amount - when it comes to pH then it will shift the pH into a potentially unsafe zone for BWB canning unless you add additional acid above and beyond the required 2 T lemon juice. Granted most of the fruits are acidic but one can only expect them to compensate pH-wise to a limited degree.

Obviously you wouldn't want to have to pressure can jams to cover the safety issue so care is required. For example the approved and tested recipes call for no more than 1/2 cup mixed peppers to 4-6 cups of fruit and also adding 1/2 to 3/4 cups vinegar to compensate.

So from a canning safety POV doing as you describe would either be (1) for fridge storage and fresh use only or (2) for the freezer. Of course nothing says you cannot add the peppers to the jam after you open the jar of jam/jelly. That option is always available. Going that route also eliminates any possible setting issues.

Dave

Thanks so much for the super fast feedback, Dave. Based on your response, I'm going to look into freezer canning. I do like a lot of heat, hence the full cup I was wanting to add, but if its not safe for BWB canning (along with me not really knowing what I'm doing yet...lol), I will take the safer route for sure. Thanks again.