Try something like this.
It assumes that you have a CSV with all the clusternames in a column named ClusterName, and that the Datacenter has the same name as the Cluster and only contains 1 Cluster.
Import-Csv -Path .\clusters.csv -Pipeline row |
Foreach-Object -Process {
$folder = Get-Datacenter -Name $row.ClusterName | Get-Folder -Name 'Appliances'
New-VIPermission -Entity $folder -Principal 'domain\user' -Role 'VM.Manager' -Confirm:$false
Get-VIPermission -Entity $folder -Principal 'domain\obsoleteuser' | Remove-VIPermission -Confirm:$false
}