Nick,
I wouldn't go the iodine route. I can see no real positive aspect to it, except for giving a totally different artiificial look to the one it has now.
The art of tsuba and nakago repatination is one of the most complex and closely guarded of all the procedures. If it was simple, everyone would be doing it, instead of a handful of professionals. There are many tips ranging from hanging up in an outdoors latrine, to the carrying in a pocket with a soft cloth, to the years worth of light rubbing. Ingredients range from nose and forehead oil to various noxious concoctions.
I believe Ford had some info on it, on the old carving path forum. I am not sure if he has posted it on his new forum yet, I will have to check. The old thread is here: http://www.thecarvingpath.net/forum/ind ... topic=1016 It is very involved and takes a real artist to get right. Anything else just looks artificial. I wish I could give you better news, but at the end of the day this is something for a professional who is an expert on the true methods.
If you do decide to give it a try yourself, make sure it is on a worn out and fairly average plain tsuba, and don't try the "quickie" methods as none are really worth much.
Regards,
Brian