There is a roadmap item slated for first half of 2025, that would allow a bulk resync of device from Control Hub. 

This can either be done per device or set as a default for all phones that are onboarded This article will explain where to find the settings for interdigit timers https://help.webex.com/en-us/article/uil72l/Configure-and-modify-device-settings-in-We...

For the device defaults you have Org wide, locations and user.If you wanted every device in your org across all you locations, then go into Control hub, navigate to Calling in the left menu > service settings.Scroll down to Device > Configure Default...

If you navigate to Device Settings ( either user based or location based ) there is a setting for Line Key label. This should change the display to EXT only . 

When a user logs into their vm for the first time, they are asked to record their name. That is the only requirement, the do not need to record a greeting, if they do not then the default messages will be played. If there is an unwanted recording of ...