Yes, in an unpatched game you can open multiple copies of the charm window, and drop a charm into each of them. However, this can cause problems with the charm window opening off screen (a minor annoyance, since it is fixable) and with a long list of charms added the game can crash if the mouse-over item description hits the edge of the screen (or it did when I tried adding something like 20 charms to an item as a test, anyway).
The charm pane exploit was fixed in the patch, but there are better and safer methods to do the same thing.
You can use
iZakaroN's SaveEditor (or from
Kiya's site, with description) to give yourself extra skill points to learn the Enchant Weapon skill, or give yourself extra stat points. Using
DAD's item editor you can add bonuses to equipment directly, rather than using charms.
There is an easy way to duplicate stackable items (virtually unlimited
restoration potions can more than compensate for deficiencies of stats or equipment).
Drag a stack out of (or into) your inventory (or container) and hold down the control key before dropping. This will bring up the split stack pane; type in a negative number and hit enter (the checkmark will be greyed out). This can also be done in the trade window.