Basically, this would be considered a cheat but as the saying goes if you are going to cheat at least do it well...
That being said this is just a proof of concept post & if it has been done and posted already I sincerely apologize for wasting your time
Firstly you need to grab Norbytes Unpacker to get to the files that needs changing ...
Let's get to work then
1 - Unpack the Istools tools into your game data folder, then use the DivinityED.exe to unpack the Main.pak placing it into the platforms folder (you do not need to unpack any others atm).
3 - If you are savvy enough you can either make a new blank mod or use an existing mod that you already have installed, for my purposes of testing I decided to use a mod call Source Difficulty I dled @ the Nexus as my Base.
4 - Goto platforms folder >> Public\Main\Stats\Generated\Data
Copy the Weapons.txt file onto your desktop, you are going to edit certain values of weapons you "already" own (meaning you should not mess with the values of weapons that have not been found yet).
For the purposes of this exercise I am just going to show you one that had been bothering me for a while & I just fixed it a short while ago ... using Notepad++ as my editor (you can dl this free software from their site) I was able to make a tenebrium based staff using the Pergamon from an early quest (I chose to keep it), also you should have completed the Brandon Quest aswell or you will Rot.
Anyway this is what I did, using search "unique" I found my target and I edited it like so >>
new entry "WPN_UNIQUE_Pergamon"
type "Weapon"
using "_Staffs"
data "Act part" "6"
data "Requirements" "Intelligence 8"
data "Damage Type" "Shadow"
data "Damage" "8"
data "DamageBoost" "100"
data "Damage Range" "5"
data "CriticalChance" "9"
data "Durability" "15"
data "Value" "10"
data "ConstitutionBoost" "5"
data "ShadowResistanceBoost" "9"
data "FireResistanceBoost" "5"
data "WaterResistanceBoost" "5"
data "AirResistanceBoost" "5"
data "EarthResistanceBoost" "5"
data "ComboCategory" "Staff"
data "ExtraProperties" "Burning,5,2"
data "Flags" "Unbreakable"
you can either copy this and overwrite the entry or customise it yourself.
5 - Then I placed my newly edited Weapons.txt into >>
D-OS/Pubic/Source Difficulty/Stats/Generated/Data
6 - To make this work I also had to copy over the "second" Weapons.txt found in the Links folder into the Source Difficulty > Stats > Generated > Links (had to make the links folder).
7 - Start new game > save as [test] > exit > goto saves (In my case since I'm running the GOG version it's in my Docs folder) look for the [test] save then copied over the meta file onto the save I was currently running.
Viola and there you have it ---- A freshly minted Tenny Staff for Jahan!