Powershell to append to an OOO that is already set

Hello,

I'm somewhat new to PowerShell.  I know how to Get and Set MailboxAutoReplyConfiguration.  What I need is a script that can Get the OOO and then Add additional text to it.  If one isn't set, then just add "I'm no longer working here"

I know it's along the lines of Get-MailboxAutoReplyConfiguration, If already set, then Export Username and OOO Message.  Else Set-MailboxAutoReplyConfiguration "I'm no longer working for XYZ Company"

I hope this makes sense.

Thanks in advance!