Frankly, it's OK to change. It is not OK to be dishonest.
See Michael Goodwin's Hillary's big lie grows (The senator needs to end the victim act and stop blaming Bush for her vote on Iraq):
"To hear the Clintons fudge now, you would think the invasion began the very next day. In fact, it began five months later, in March 2003. During those months, as U.S. troops massed in the Mideast, there is no record of Hillary Clinton opposing the invasion or claiming she had been misled."
Hillary was not misled. Instead, she is misleading us now!