Snapshot migration depending on class of member field

I have a class stored in snapshot say class A(member: MemberClass). MemberClass is a trait with multiple classes extending it, say MemberClassA, MemberClassB, MemberClassC. I would like to add a mandatory field to MemberClassC. The value is derived from another field of the class.

How would I do it? If using Jackson Migration I would have to have a way to check if member’s type is MemberClassC. What is the best way to do it?