Canning safety question- pickle recipe for relish?

So, I want to make watermelon relish using a recipe I have used and loved to make watermelon pickles. I want to make 2 changes and that is A: the size of the watermelon rind pieces & B I want to add diced jalapeño.
The pickle recipe (from the Ball Complete Home Preserving book) specifies that the rind should be cut in pieces 1” X2”.
For my relish, I want to cut the rind to bits 1/4”X1/4” and want to add jalapeños diced to the same size. The ratio of brine to rind/pepper would stay the same as in the recipe. The jalapeños are currently frozen, but the rind is fresh. The canning directions are for water bath canning
So. Can I safely make either of these adjustments and still can it all in a water bath?
Thanks!

Here’s the recipe I’m working from.

Personally, I don't see why not, with the amount of both sugar and vinegar, in there. I would likely try it, but that's me taking my own risks. I can't advise you, really. The only thing I can think of that you might run into would be softer melon rind pieces. The pepper would not likely mess with the recipe at all, as far as chemically - unless it was to improve it - I think.

Adding another food that can be vinegar pickled will not change the safety of the recipe- so no issue with adding the pepper. However the size of pieces does matter for food safety, because the more gel-like the food is the harder it is for heat to penetrate. (I learned this in Culinary Arts College)

"If the food is thick, puréed, or mashed; if there are large pieces of food in the jar; or, if the food is packed in too tightly, heat penetration can be slower than in more liquid or loosely packed foods. If a specific heat process is not calculated for each food and style of pack, the heating may not be adequate, and the food will be underprocessed." --source

The standard accepted safe work around for this is to can it exactly as directed, and then blend it all when you open the jar to use it. Since unsafe home canned food can kill you, I always go with the approved safe way , even though I'm a kitchen rebel who almost never follows a recipe in any other situation.  

Alternately, you can puree it and *not* can it, but instead cook it in a pan and store it in the fridge if you intend to use it in the next couple of weeks.

This is essentially a relish recipe:
Marilyn’s Green Tomato Pickle

5lb green tomatoes, chopped
2+1/2 lb onion, chopped
1/3 cup salt

3cups white sugar
2+1/4 cups apple cider vinegar
2 oz pickling spice in cheese cloth bags

1+1/2 tbsp. coleman's dry mustard
1/4 tsp cayenne pepper

Place chopped tomatoes & onions in a large pot. Pour salt over, press and let stand over night.

Next day, add sugar, vinegar and stir to mix with juices. Add in the pickling spice bag(s).

Boil 1&1/2hours to reduce liquid. Remove from heat.

Stir in mustard and cayenne thoroughly. Scoop into sterilized jars and process 12-15 min.

According to the web "5 lb equals 11.3 ( 11 1/3 ) cups" as related to chopped tomatoes, so the ratio of acid to fruit is much higher on your recipe, however, tomatoes likely are more acidic than watermelon rind, which would also factor into it.

I think I'd try g--gling a variety of "relish" recipes, and maybe search relative acid content of fruit/veggies used.  After all, someone had to take a chance at some point when developing recipes. We don't want any dead permies, for sure, but we've also seem to have gone through a period of trying to convince people that meeting their food needs, has to depend on technology and big factories, and I've read about a number of recalls that have happened when some big factory or other screwed up! I think that with a reasonable amount of research, you could come up with a safety factor you're comfortable with. I know that when I've done something a little iffy, I've let the boiling water bath go 15 minutes instead of 10 and that was with the 500 ml bottles - the bigger the bottle, the longer to give it if you're experimenting.

I chop mine to 1/4 inch cubes. I have no problems with it.
The canning books are written for "this is the recipe we tested" and most people want bigger chunks of melon. It's like any other pickles, you can make any pickle or pickle relish work if you use the right ratios of vinegar, and process it a bit longer if you want to, I have never seen over-processed kill anything. Might be not quite as perfectly crunchy, but I don't care, I'm not into the crunch. I am more into the flavor and often end up cutting up stuff I canned bigger because I need it smaller for what I'm doing anyway.

I'd say 1/4 x 1/4 is fine. It won't look as cute if you are entering it in the fair.
And jalapenos will not change it either. They add flavor but don't affect the basic recipe ratios.

I google "Watermelon Relish" and found several of recipes from reliable sources.

None of the recipes stated size as most just said, "Diced Watermelon Rind".