Convert All Underlines to Italics in Under 1 Minute (and Vice-Versa)

The Problem: Readers prefer accentuated words to be in italics, but editors/publishers prefer them to be underlined.

Reason: Italics are naturally smoother to read, so the eye skims over them easier. When preparing a document for publishing, underlines are necessary so the typesetter's eyes can pick out the accentuated words easier, and know which ones should be set as italics and which ones should be normal.)

The Question: How do I quickly convert all the underlined words in my document to i...