Just got some amazing work done on my weapon and (as always) re-registered it to it's newest form. Please remember to REGISTER and MARK anything you care about.
You should re-register an item any time it changes, name, weight, enchant, etc. MARKing an item makes it unsellable, which is super important when sifting through junk. You can unmark items later.
Borrowing a friends item? REGISTER IT! it's not a mark of ownership, it's simply a bookmark for GM's should anything untoward happen. Register often, Register always.