I am not one to strictly follow a recipe.  I rarely like to use true measurements.  I like to adjust as I go and learn along the way for what tastes best to me and my family.  I have learned that I don't have this liberty with canning.  There are acid levels and boiling times and more that need to be followed precisely to prevent spoilage.  I am not willing to let the hours of effort and work I put into canning go to waste just because I wanted to experiment!  (Not yet anyway.  Maybe some day I'll be confident enough to branch away from the recipe!  In the meantime, if anyone is looking for a present for me, may I suggest the Ball Blue Book, 100th Anniversary Edition. Complete, comprehensive guide to home canning, freezing and dehydration.)

One rule that must be followed, yet has room to play when canning salsa, is the number of peppers cannot be changed, but the type of peppers can be adjusted to fit your taste.  My husband loves spicy, hot salsa.  He walks away from mile, even medium salsa.  So when the recipe I tried called for 5 red bell peppers, I used 5 other hot peppers like Serrano and Hot Banana.

Canning how to and resources:
Let's Preserve: Canning Basics
Canning Tomatoes and Tomato Products
20 Canning Tips - Timeless Wisdom Collection

Salsa recipes and canning tips:
16 homemade salsa recipes and canning tips- be sure to see all the great links after the recipe list
Canning Tomatoes: Roasted Salsa