When saving BulkData, if we are overwriting the file we need to update the BulkData's (flags,offset,size) to be able to load from the new file. But SerializeBulkData modifies those values when loading, so the in-memory values after loading from disk are not the same as the values on disk. This function handles running the same steps that SerializeBulkData does, but skips the deserialization of the BulkData.