((a)) An appropriation available to an agency may be charged at any time during a fiscal year for the benefit of another appropriation available to the agency to pay costs—
((1)) when amounts are available in both the appropriation to be charged and the appropriation to be benefited; and
((2)) subject to limitations applicable to the appropriations.
((b)) Amounts paid under this section are charged on a final basis during, or as of the close of, the fiscal year to the appropriation benefited. The appropriation charged under subsection (a) of this section shall be appropriately credited.