I don't think that redistribution is such a great risk, especially if one is continuing to chelate. Without chelation, greatly increased mercury excretion from taking several mg a day of iodine occurs. What mercury that is unbound and not excreted immediately will probably be excreted in the next chelation round. The important thing is that it is going to a more loosely bound state, so that it is on the way out of the body. Many who have mercury toxicity and thyroid problems probably have plenty of mercury clogging up the iodine binding sites on the thyroid.
Taking several grams a day of iodine seems to help dislodge this mercury and other toxic heavy metals from the thyroid. Those who are mercury toxic may also have elevated levels of lead or other toxic heavy metals, as the mercury overwhelmed the natural detoxification channels for excreting heavy metals.