The Office of Extramural Research at the US National Institutes of Health has allowed multiple investigators on grant applications since 2007 "to promote team science and multidisciplinary approaches to biomedical research," says the office's Extramural Nexus publication. Though a request for multiple principal investigators was only allowed on new or renewal applications. The policy has now been revised to allow changes mid-award. "We determined that unique circumstances may arise in which it would be in the best interest of a project to change the leadership model mid-award, and that peer review of the new leadership team and leadership plan may not be essential in these cases," the post says. The notice may be seen here.