handling list as entity

[mrgleeco]

First off, thanks for this package! In my use case, it works almost too well.
Say i have two sources, each with a list property:
source.A:

group_members:
  - alice

source.B:

group_members:
  - bob

what i end up with by default is a list ["alice", "bob"]. I'm wondering if there is any way to treat lists as a whole, such that if i merge A then B, that source.B list is exclusive (ie just bob)?