Accents/Special Characters

I'm looking for a grep or script that will allow me to put accents on letters.  For instance, taking e and making it ē with the macron above it.  Our authors indicate they want this by indicating it this way:

e[set macron over e]

At this point, I have simple find/replaces loacking all of those and replacing them with the ē.  It's the same for every letter asking for a specific accent above.

I'm hoping to figure out a grep or script that will keep my find/replace list from getting too big.  At this point, I've got 35 find/replace just to locate these, and my list is growing every time I encounter another accent.  Considering how much each letter has...

Anybody know of a simple way to do this?

Thank you!