At any time during the fiscal year the Manager may transfer part or all of any unused appropriation balance among the programs within a department, office, or agency. Upon written request by the Manager, the selectmen may by resolution transfer part or all of any unused appropriation balance from one department, office, or agency to another. Notwithstanding the above, no unexpended balance in any appropriation not included in the budget of the selectmen shall be transferred or used for any other purpose.