Yo long time ago there was a bug that prevented players from getting damage when they wore a set of diamond armor with protection 4. I actually enjoyed this bug because it made long fights without having to use gapps or potions possible. My question is, is there a way to change the code of the old armor strength module so there won't be damage until one armor piece breaks?

That's not really within the scope of this plugin - if it was a bug it would have to be fixed. However, now that I am finishing up fixing all of the various damage interactions there may be more flexibility in configuring the individual damage / protection values.