Section 4. The governing board may accumulate so much of the annual net income of an institutional fund as is prudent under the standard established by section eight, and may hold any or all of such accumulated income in an income reserve for subsequent expenditure for the uses and purposes for which such institutional fund is established or may add any or all of such accumulated income to the principal of such institutional fund, as is prudent under said standard. This section does not limit the authority of the governing board to accumulate income or to add the same to principal of an institutional fund as permitted under other law, the terms of the applicable gift instrument, or the charter of the institution.