You should be able to create a utility user for this using AMP’s permission system:
https://discourse.cubecoders.com/t/managing-user-permissions-in-amp/2301
Though you could also just run a script as the amp Linux user to preserve file permissions, or alternatively use the AMP API to update smaller files (there’s a download-from-url API method too). More info surrounding the API here: https://github.com/p0t4t0sandwich/ampapi-spec