PowerCLI

I have already a script that compares existing privileges with a TXT file and adds a missing ones.

Solved: Cmpare Privilege based on TXT file - VMware Technology Network VMTN

I have come to the conclusion that there may be privileges already added but not necessary for the role.

Is there a way to remove privileges that are not mentioned in the text file?

Wouldn't it be a lot easier if you just remove/add the role when it already exists?
No fiddling with adding/removing proivileges.

I have considered this, but I am aware that the current role may already have assigned users.

Ok, the following should handle all cases.

Note that the call to the UpdateAuthorizationRole method might return sooner than the changes are actually applied.
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$Pfile = .\Folder\Plist.txt

$PList = Import-Csv -Path $Pfile
$privs = Get-VIPrivilege -Id $PList.LIST
$authMgr = Get-View AuthorizationManager

$sysPrivs = 'System.Anonymous','System.Read','System.View'

$existingRole = Get-VIRole -Name $NewRole -ErrorAction SilentlyContinue
if ($existingRole) {
    Write-Host "A role with the name $NewRole already exists."
    $currentPrivileges = $existingRole.PrivilegeList | Sort-Object

    $missingPrivileges = $PList.LIST | Where-Object { $_ -notin $currentPrivileges }
    $extraPrivileges = $existingRole.PrivilegeList | Where-Object { $_ -notin $privs.Id -and $_ -notin $sysPrivs}

    if (!$missingPrivileges -and !$extraPrivileges) {
        Write-Host "The role $NewRole has the correct privileges:"
    } else {
        if ($missingPrivileges) {
            Write-Host "The role $NewRole is missing the following privileges:"
            Write-Host ($missingPrivileges -join "`n")
        }

        if ($extraPrivileges) {
            Write-Host "The role $NewRole the following extra privileges:"
            Write-Host ($extraPrivileges -join "`n")
        }

        # Correct the privileges
        $authMgr.UpdateAuthorizationRole($existingRole.Id, $existingRole.Name, $privs.Id)
        Write-Host "The role $NewRole now has the correct privileges:"
    }
} else {
    New-VIRole -Name $NewRole -Privilege $privs
}