help with a general manager
I'm at a loss for words why a GM would want to make changes in your absence instead of dealing directly with you to redevelop recipes etc. it would seem their social skills are underdeveloped if they are in fear of conflict even though they are the "top dog".
best solution is meet with the GM more regularly to improve communication and hopefully get more changes done in collaboration as a team rather than working independently of each other.
you both have the same goals which is to make the best product to suit the market, at the lowest cost. more understanding of what is wanted to suit the market may open your eyes to what the GM sees as important from a business perspective and how that relates to what you see as important as the creative mind behind the product.
if communication cant be improved then the situation wont change and decisions will need to be made if you allow the changes to occur, or you do not like the arrangement and seek a more rewarding position elsewhere.