What if I don't have all the bricks enabled and I still want some of the bricks that did not load to "exist".
If there isn't a callback for when a brick fails to load, you could go through the file with a whitelist of UI names that are on the server, but then you still have to think of a way to determine per-brick ownership through the save file.
You have two options the way I see it, either half-ass the ownership through bls and load it anyway, or do a good job on the bls ownership detection and have it convert the entire save file. My advice is to do the latter