Yair,
just make a short list of keywords in LR. Make different types and
the export it: METADATA -> EXPORT KEYWORDS
now you have a text file which you edit. The syntax in the text file is
very simple and should be clear when comparing to what you have in LR.
Make some changes in the text file and import it back to LR. You'll see
what works. METADATA -> IMPRT KEYWORDS
BUT, how not to loose the old keywords?
Kirmo