Subscribing lists to each other

We have application A with two lists, that we want to subscribe to two lists in application B with conversion logic (concatenation mainly, but also adding properties that are defaulted for integration purposes).

In application B we then build a hierarchy not subscribed to anything but completely unique, based on the original two list values coming in from Application A.

Now I see that only Add/Delete are options when subscribing lists to one another. My questions:

1 - Why would the other actions (modifying members) only be available for hierarchies?

2 - is there a way around to reflect changes made to the members also in the lists in application B?