参考:https://social.technet.microsoft.com/wiki/contents/articles/18661.sharepoint-2010-update-a-permission-level-using-powershell.aspx
$sites = get-spsite -Limit ALL –webapplication http://mywebapplication.com
ForEach ($site in $Sites)
{
# The URL to the Site Collection
$spWeb = $site.RootWeb
# Enter the Name of the Permission Level to Change
$PermissionLevel=$spWeb.RoleDefinitions["CustomOwner"]
# Enter all the permissions that Permission Level should have enabled
$PermissionLevel.BasePermissions="ViewListItems, AddListItems, EditListItems, DeleteListItems, ApproveItems, OpenItems, ViewVersions, DeleteVersions, CancelCheckout, ManagePersonalViews, ManageLists, ViewFormPages, Open, ViewPages, AddAndCustomizePages, ViewUsageData, CreateSSCSite, ManagePermissions, BrowseDirectories, BrowseUserInfo, AddDelPrivateWebParts, UpdatePersonalWebParts, UseClientIntegration, UseRemoteAPIs, ManageAlerts, CreateAlerts, EditMyUserInfo, CreateGroups, EnumeratePermissions"
$PermissionLevel.Update()
$spweb.Dispose()
$spsite.Dispose()
}