Hi Shane, 

The beef stew recipe is published in multiple Ball books, but I am having trouble locating the place where that specific modification is listed. Do you know which edition you are using? 

In general, you have to handle modifications of pressure canning recipes very cautiously. The safety of the final product absolutely depends upon adequate heat transfer during processing, and heat transfer can be affected by the size of the pieces in the jar, the amount of liquid, the density of different vegetables, the balance of fats and proteins, etc. If the Ball book does not specifically allow for a modification, you should avoid making that modification. 

If you want a more flexible soup recipe, take a look at the NCHFP soup recipe. This recipe was written with a wider safety margin that allows you to swap out different meats or vegetables to your taste. You must use only vegetables or meats that have their own processing instructions from the NCHFP, and you must fill the jar only half full with solids (topping off the rest with broth). This recipe also does not allow for any thickeners (flour, starches, rice, noodles, etc.). 

Thanks for using Ask Extension,

Jared