Change default variable of BP children at compile time (like construct script, before spawning)

I’m trying to assign unique ItemIDs on Blueprint types without having designers do this manually per BP.

The idea was to have a default of -1, int32 ItemID. On construction check all the child classes of InventoryItem and see what the first available ItemID value is (eg. highestID + 1)

The problem is that construct script seems to be for spawning of Actors, I’d like to run mine at compile time only (the items are not spawned in the world, I don’t want to adjust instance variables, but change the BP defaults for every BP child class)

Thanks for any help! (Or even a simpler alternative would be great!)