Repeat a mail merge field

This is a pretty specific question but I think it belongs here.

I have a Word document with tags surrounded in <<brackets>> that I have to replace using mail merge. I am using Office 2007. It took me a long time and the help of a coworker to even figure out how to do this in 2007 because he trained me in 2003. In 2003 after you do one occurrence you can do all the others with ctrl-y. If I hit ctrl-y in 2007, it replaces the same one I just did over and over. I found and tried all the possible "repeat" key combinations and they all replace the same one I just replaced. Does anyone know how to do this?

If I'm not explaining myself properly, what I want to do is merge <<Last_Name>> with Last_Name which may appear 10 times in the document. If I can do it just once and repeat it 9 times, that would speed up the process a lot.

Thanks...