Citigroup's Thomson, Krawcheck Swap Posts  NEW YORK (Reuters) - Citigroup Inc. &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=C.N target=/stocks/quickinfo/fullquote"&gt;C.N&lt;/A&gt; on Monday said  Todd Thomson, its chief financial officer and head of strategy,  will swap posts with Sallie Krawcheck, Smith Barney's chairman  and chief executive officer.