I don't know the answer to your question but I'm curious why you need the
cursor to move only a 1/2 space. I've only had to do that on a typewriter
when I'm trying to get text to fit, something I don't need in Word.
If you're just being picky about word spacing in regular text, use the
Format > Font > Character Spacing dialog and set the spacing to a
negative value, such as -2 pt.