UObject Lifecycle | When to access subobjects of blueprintable UObjects

I have 2 blueprintable UObject classes for an inventory. (inventory and item)

For efficient replication I mark my objects to need replication with a replication key. For that the item will need a reference to the inventory.

In the blueprints I can add Items to the inventory. I need a way to set the Owning inventory for each item before the object is further used. In the constructor I don’t have access to the in blueprint added items.

I considered PostInitProperties(), PostLoad(), PostCDOContruct() and PostCDOCompiled(), but none of these seem to serve my purpose.