A few notes on this trick:
1. Each item that you want to use has to be unique to your inventory. For example, after you have done the trick with the ring of wizardry, you cannot do it again. In other words, each time you find a unique item in the game, you can do the trick once. OR if you get some sigil stones, you can make rings and amulets with unique names and do it all you like.
2. As usual, you cannot do it with armor, only rings and amulets.
3. If using bows, be sure you have a very high count of arrows.
4. Sometimes the effects are messed up: I added two +125 feather rings this way and I only got +8 on one of them.... Maybe that is the max my person can carry, but the rings are supposed to be independant of that.
5. Don't do this trick with anything you may want to remove later, like life detect or night eye.