Weapon upgrade question.

I have an axe that legthens crippled duration, has dmg bonus when health is less than 50%, and armor +4. I would like to change the upgrades on the first two, but I don't want to mess w/ the armor. How do I know what upgrades (haft, handle etc.) will change those and which one would change the armor bonus? Also on things like "lengthens crippled duration" and l"engthens weakness," does this mean that an attack you have w/ this weapon that causes crippled will just be longer or what.

the +4 armor is probably the axe grip.