I don't think there is any official certification for master craftsmen. Probably earned through experience and volume of bats produced. If you have learned all aspects of bat making and are good enough to train others, I think you call yourself a master bat maker. Unless you are associated witha big label or have an established brand of your own, I doubt the self certified title will mean much though.
SS factory in India is full of master craftsmen/batmaker, some who have been making bats for generations.