With snapd version 2.41 (currently in candidate channel) the snap and snapctl commands will get the long-awaited support for unsetting of configuration values. Both commands will now have unset sub-command that takes a list of configuration options to unset. Unsetting will also be possible with set sub-commands by giving it configuration options followed by exclamation marks. The latter allows for mixing setting and unsetting in one go. Examples:
With snap command, for snap users:
snap set mysnap port.https! port.http=80 # unsets https port, sets http port
snap unset mysnap port.https port.http # unsets both options
With snapctl command (for use in hooks by developers of snaps):
snapctl set port.https! port.http=80
snapctl unset port.https port.http
Please see the documentation for more details regarding snap configuration: