The Disaster Management Costs Modernization Act amends section 324 of the Robert T. Stafford Disaster Relief and Emergency Assistance Act to give states, Indian Tribes, and territories the ability to reallocate excess funds for management costs from closed disaster recovery projects to other recovery activities. It defines excess funds for management costs as the difference between the authorized amount and the actual expenditures at the time a grant is closed. These funds may be used for capacity‑building activities, disaster preparedness, mitigation measures, or other management costs related to major disasters or emergencies. The provision applies only to grants awarded for disasters declared after the act’s enactment and funded with appropriations from that date onward. The President may make these excess funds available to grantees or subgrantees under sections 403, 404, 406, 407, or 502, and the funds remain available for five years from the date of release. No additional appropriations are authorized for the amendments, and a GAO study must be submitted within 180 days to assess whether the set‑aside amounts for management costs are appropriate. The study will report on past management cost allocations, usage, and disaster durations to inform future budgeting decisions.