So I whipped this up quickly, but CamStudio had a few hiccups and looks like it is running on a toaster when I was fine on my computer. Having problems opening the file for editing so just uploading the thing as is, hopefully you can still use it.
Watch me curse myself by putting on Havel's Ring: • Curse by Havel's Ring
Check out my Pastebin, then Weapon Properties for some explanation as to what I am doing
http://pastebin.com/mEvsWKx2
Essentially, the value for Havel's Ring is 262144000. That is its Model + Icon number across 4 bytes (they take up 2 bytes each, next to each other).
By browsing that memory region, 2 addresses above the found Model ID address is the value for storing Ring Effects.
I had already manually added that address to my table, though it only needs to point to it as a 2 byte type, so I could easily change this value to other effects. In this video, that is changed to the Calamity ring so you could visually see a change.
Havel's ring is the top of the list, if you scroll down you can see all the other rings in the same format. The Calamity Ring is the last ring.
There are 41 rings in game, however the Icons for rings starts at 4000 (Havels) to 4043 (Calamity), so there might be 3 rings in there that aren't meant to be available for players.
Most likely the value were reserved, and they probably aren't in the game.
Then again, I did find Gwynevere's Talisman Model and we know the ID exists for that, there are also icons for other items that are not in game, so who knows what is hidden in the files.
Also, the values for Ring Effects goes from 2000 to 2350, lots of room for potentially extra hidden effects (as is known for Weapon Effects).
Watch video Dark Souls - Modifying Rings with CE online without registration, duration hours minute second in high quality. This video was added by user Twools 18 March 2013, don't forget to share it with your friends and acquaintances, it has been viewed on our site 6,70 once and liked it 1 people.