Canning Meat With Added Vinegar
ANSWER - Adding vinegar might make the meat more tender although the extremely long heating times should make a tender product. although adding vinegar will not make this product become unsafe, we do not recommend that consumers modify the recipes in the USDA Complete Guide to Home Canning. Some other modification that a consumer might make could cause the product to become unsafe to eat.
See this link for information, read Penn State Extension's Let's Preserve Meat and Poultry.