You cannot add in more peppers, but you can substitute the type of peppers. This salsa recipe for canning uses 2 1/2 cups of chopped bell peppers along with 3-4 medium jalapeños. If you want more heat, then I recommend subbing in some of the chopped bell peppers for spicier peppers. When I make this hot, I usually add 2 cups of chopped bell peppers and 1/2 cup of chopped jalapeños.