You can, but this will alter the flavor. Taco Bell's recipe uses jalapenos and vinegaru002du002dUsing pickled jalapenos and their juices helps cover both of those. If you use fresh jalapenos, add 1-2 tablespoons of vinegar as well. The fresh jalapenos will be spicier than the pickled jalapenos as well, so either reduce the amount by half or be prepared for a hotter sauce.