In this new update mode, a set of base DATs can be used as a replacement naming scheme for the input DATs. Only the item names will be updated, so this willl not fill in additional hashes or the like.
This is the same diffing that is used by Romba to output its diffs. It is currently untested. Basically, this will take a set of base DATs as an input, and then diffs all of the individual DATs against that combined base and then outputs accordingly.