Regulated Investment Company Modernization Act of 2010 - Amends the Internal Revenue Code, with respect to regulated investment companies (RICs), to: (1) allow an unlimited carryforward of the net capital losses of RICs; (2) eliminate restrictions on the investment of RICs in commodities; (3) limit penalties for the failure of RICs to satisfy gross income and asset tests; (4) modify rules for allocating RIC capital gain dividend distributions; (5) include certain nondeductible items of RIC income in earnings and profit calculations; (6) allow RICs that invest exclusively in the shares of other RICs to pass through to their shareholders tax-exempt interest and foreign tax credits, without regard to certain investment limitations; (7) modify rules relating to the declaration of RIC dividends, return of capital distributions, and stock redemptions; (8) allow certain RICs with shares that are redeemable upon demand to treat distributions in redemption of stock as an exchange of fund shares or a dividend for tax purposes; (9) allow a deferral of end-of-year losses of RICs; (10) exempt certain regularly declared exempt-interest dividends of RICs from holding period requirements; (11) increase the annual amount of capital gain net income of RICs required to be distributed; and (12) modify excise tax and penalty rules applicable to RICs.