Hi mate, If I understood your question then the answer should be even easier. To take a stat from another item you just have to edit the stat string from the root template manager.
The root template manager should be open at the start of the divinity engine, otherwise you can just run it from the toolbar above, is one of the buttons on the left side.
With the root template manager up and running just click on the icon "open" at the top and it will load all the datas from the main game. Look for the item you want to change the "stats" from and on the property panel just scroll down till you find the string "stats", just edit it clicking on the "..." and select the "stats" you want to use.
if you struggle by following this little tip, when I get back home from work, in the evening, I will add screenshots as well, obviously if nobody comes first assisting you in the proper way :P