Overwriting Catalog vApp Template using PowerCLI

Hello,

     I cannot locate the cmdlet and parameter to overwrite an existing catalog item (vApp Template) using PowerCLI. I can add one without issue using the 'New-CIVAppTemplate' cmdlet, but that has not option to overwrite. Nor does the cmdlet 'Set-CIVAppTemplate'. Did I miss it, or is it not possible using PowerCLI?