How can I put a macron over the letter “m” in MS Word

KeyRemap4MacBook

A preference pane with currently about 1500 remapping options. Includes Backquote(`) to Escape and Escape to Backquote(`).

Ukelele

You could create a custom .keylayout like this:

Esc on the layout above worked with all of the things I tested:

• OS X UI actions like canceling a dialog and exiting full screen
• On some websites with keyboard navigation like Google Search
• As a meta key in Terminal.app

Modifying special keys from a .keylayout usually results in some unexpected issues though.

The accented character selection when a key is held was one of the tiny things that changed in Lion. To disable it, run this in the Terminal:

defaults write -g ApplePressAndHoldEnabled -bool false

I will admit, though, it is strange that there's a setting in System Preferences that only affects behavior accessed through a defaults write command.