It does not seem possible to change the default action for an application filter once it has been created. While there may be little need for this in most use-cases, it would be tremendously helpful for one-off testing.

Allowing to set application bandwidth based on the percentage of the WAN bandwidth available will make enable copying configs from firewalls with different total WAN bandwidth. Moreover will make it a less hassle to upgrade or downgrade WAN bandwidth in the future. This feature would greatly enhance the settings for MSPs or vendors who send out pre-configured firewalls.

Allow us to 'exclude' certain applications which may not be able to be configured on an IP/port basis, from the Quota functionality.
E.g Skype, Viber, Skype4Business, Office365

Also, Windows Update and other software update that may consume quota quickly.