I have Yealink phones which have the ability to upload the config file back to the FreePBX server when the users makes a custom change. Such as the user setting their own custom speed dial or BLF key.
We have done this in the past with Polycom phones. The only way we were able to do this for our phones was if the provisioning server was an FTP server, not an HTTP server. The phone would then use the FTP credentials to upload settings (and phone logs) to the directory in question.