This script updates all scopes of all authorized DHCP servers in a domain to use specified dns update credentials, to always update dns records and to set maximum lease duration

Unify-DHCPScopeSettingsInDomain.ps1

$dhcpServers = Get-DhcpServerInDC
$Credential = Get-Credential
$days = Read-Host "Maximum lease duration in days (scopes with longer periods are set to this value)"
$timespan = New-TimeSpan -Days $days

foreach ($dhcpServer in $dhcpServers) {
    Write-Host $dhcpServer.DnsName
    Set-DhcpServerDnsCredential -Credential $Credential -ComputerName $dhcpServer.DnsName
    Write-Host "   DNS Update credentials set"
    $scopes = Get-DhcpServerv4Scope -ComputerName $dhcpServer.DnsName

    foreach ($scope in $scopes) {
        Write-Host "   $($scope.ScopeId)   $($scope.LeaseDuration)"
        Set-DhcpServerv4DnsSetting -ComputerName $dhcpServer.DnsName -ScopeId $scope.ScopeId -DynamicUpdates "Always" -UpdateDnsRRForOlderClients $True -DeleteDnsRRonLeaseExpiry $True

        if ($scope.LeaseDuration -gt $timespan){
            Set-DhcpServerv4Scope -ComputerName $dhcpServer.DnsName -ScopeId $scope.ScopeId  -LeaseDuration $timespan
            Write-Host "      lease duration updated to $timespan"
        }
    }
}