Deploying files into the users home/Library folder impossible due to insufficient permissions

I am trying to deploy a Powerpoint template to the proper directory (/Users/<username>/Group Containers/....) on all managed Macs. Copying the template into the /tmp folder on the Macs works, but.... When I execute the post download script, the copying / moving (with cp or mv) to the proper directory fails due to insufficient permissions of the destination folder (/Users/<username>/Group Containers/....). However, the script is executed as root. So the permissions should be sufficient. But still it does not work.  I researched a little: it might be that this is connected to the security measures on OSX Sequoia. My question: Is there any way to copy the template into the intended folder? Any special tricks with MobiControl? Any hint?