Sequestration Flexibility Act of 2013 - Amends the Balanced Budget and Emergency Deficit Control Act of 1985 (Gramm-Rudman-Hollings Act) to authorize the head of any federal department or agency to transfer amounts within that department or agency for FY2013 or for FY2014 in order to lessen the effect of a presidential sequestration order for that fiscal year on such entity's program, project, or activity. Prohibits such transfer from causing any account to be at a higher level than it was before such sequestration.