what about replace all (CTRL-H)
you can replace for example "i = j;" by "j = i;"
you can use regular expressions in that dialog. I'm not so sure about how you should pop-up help about them however. In that dialog, press F1, then search that page for more information on regular expressions.
I like this dialog because it allows you to go through each replacement. Because the chance of breaking something is high, I think this is a more secure solution