Thanks Jeff. No actual test data but you would be right in presuming that if you change the type of a column that is indexed, either as the key or part of the key, you will cause the index to be affected. Although this was not the point of the original question it is a noteworthy consideration.

To avoid the kind of log pressure that would result might be the reason that some folks have taken to dropping affected indexes, doing the change, and then recreating the index. Also this might affect indexes that most folks don't think of as indexes: Foreign Keys.