Is it possible to rid of the red warning that is shown when a license expires?
Where are you seeing this ?
If in the Web UI or FSM, the only way I see would be to have a License Key which does not include the expired feature.
You can contact Customer Care and see if they can help with getting that key.
I see it any time I log into the Web UI, I still have a valid live security subscription but i had a license key for the web blocker and that expired which is fine.
Customer care can remove the old trial or license for you. Click the support center link on the top right of the page here, and create a case online. Select Customer Care as the case type when it asks.
Be sure to include the serial number of the device in question.
WatchGuard Customer Support