You mean actually replacing the cover so that the inner pages stay intact? You didn't tell us what country's passport you have, but I doubt this is possible anywhere.

That said, just being dog-eared or scuffing up the barcodes to the point that they can't be scanned doesn't invalidate the passport. Just get the plastic slip cover now to prevent further damage, and expect to wait a little longer at borders as they hunt'n'peck your passport data into the computers instead.