It would take less time to copy the identical file over the existing file than it would take to read both files and check that they are identical in order to skip doing the copy. You gain nothing, in terms of changing what "Identical" means for the Skip Identical option.
You can also already set up diff/comparison tools to run them from the Replace dialog, which lets you use get a much better comparison than just a hash: Compare files from 'Confirm File Replace' dialog?