I guess you can always suppress/delete the linked exterior feature from the part navigator of the main assembly (where you created the linked exterior)
it's not that we want to delete or suppres the linked exterior.
Whe want to have it still in the tree. butt not that it updates any more.
Ok..sorry i misunderstood your question then. Can you try using EDIT/FEATURE/REMOVE PARAMETERS on the linked exterior objects. It will turn them in dumb bodies.
I have tried the edit feature, butt here is no option to break te link.
Remove Parameters can work.
It's creates single bodies of the linked exterior.
this can work.