No you cannot and should never freeze milk in a Mason Jar.
When you freeze Milk in a Mason Jar the Mason Jar will crack due to the expansion of the milk in the freezer.
Even if you have milk in glass jars that the milk comes in the milk should never be frozen in glass jars.
Always freeze the milk in a plastic jug or plastic container and never in glass jars.
Freezing milk is okay to do to preserve the milk and make the milk last longer.
However in my own opinion freezing milk is not a good idea because when you do freeze the milk the milk changes in tastes.
Some people don't mind the taste of frozen milk but other people including myself find frozen milk disgusting tasting.
I once decided to freeze some milk and then thaw it later but hated the taste and will no longer freeze milk.
I just buy milk when needed and use the milk up before it has a chance to go bad.
Frozen milk will not harm you but frozen milk tastes a lot different than fresh milk.
When you freeze milk the frozen milk should last for up to 6 months.
When thawing frozen milk make sure to thaw the frozen milk overnight in the refrigerator.