Would like to automate this Powershell command that sets the UPN of all mail enabled users

I have command that changes the UPN of all mailbox users

Get-ADUser -Filter * -properties homemdb | where {$_.homemdb -ne $null} | ForEach-Object ($_.SamAccountName) {$CompleteUPN = $_.SamAccountName + “@contoso.com”; Set-ADUser -Identity $_.DistinguishedName -UserPrincipalName $CompleteUPN}

The command works using the AD module for powershell. What I would like to do it write a script that does the following.

Runs the command above

Only applies changes to users that need it. (I think this applies the setting to all users with the "homemdb")

I was thinking of setting it as a scheduled task on one of the Domain Controllers. Mypowershell skills are lacking at best, so any guidance on how to set this up would be much appreciated. 

Thanks