You mean something like this
$esxName = "MyESX"
$dnsSrv = "192.168.1.1","192.168.1.2"
$ntpSrv = "192.168.1.3"
$esx = Get-VMHost -Name $esxName
Get-VMHostNetwork -VMHost $esx | Set-VMHostNetwork -DnsAddress "192.168.1.1","192.168.1.2"
Remove-VMHostNtpServer -VMHost $esx -NtpServer (Get-VMHostNtpServer -VMHost $esx) -Confirm:$false
Add-VmHostNtpServer -VMHost $esx -NtpServer $ntpSrv
Note that this will remove the current NTP server and replace it by the one(s) defined in $ntpSrv