[whpalmer4]

I don't know of a way to do it in one operation, but you can use the Find and Find Next commands (cmd-F and cmd-G respectively) to walk through the document and apply/remove your styling with cmd-I (italic), cmd-B (bold), and cmd-U (underline). Go to the top of the document and click on the first row, press cmd-F, enter your search string, press return, and you should be taken to the first instance in the document. Style the word, press cmd-G, repeat until you get to the end.