Disaster Management Costs Modernization Act This bill authorizes the President to allow recipients of certain disaster relief assistance to use excess management cost funds for (1) building capacity to prepare for, recover from, or mitigate the impacts of a major disaster or emergency; or (2) management costs associated with other major disasters, emergencies, disaster preparedness measures, or mitigation activities. (Management costs cover indirect costs, direct administrative costs, and other administrative expenses associated with a specific project under a major disaster, emergency, disaster preparedness, or disaster mitigation activity. In some cases, the amount provided for management costs may be more than the amount expended, resulting in an excess.)