I faced this situation from time to time that some modpacks will remove mods. Some mods provide tools and armor, and sometimes they get removed.
Most times the armor is highly enchanted which is the reason for...
A mod that has blank version of all sets. No damage, no durability (won't break), no armor defense, no use. Can still be equipped, but provides nothing but the enchantments.
It should work as a player logs in or as server starts.
Ex: If a tool/armor existed but no longer it replaces the tool/armor with a blank version keeping any enchantments it has.
This is particularly useful if the modpacks has a mod that can extract enchantments.
This mod idea could also be configured to instead of blanks it uses enchant books. For modpacks without a way.