Keep customized system messages sending automatically without needing a trigger

When I use Change Message on a system message (for example Send Confirmation to Guest or Send Receipt to Guest), the saved custom version no longer sends automatically unless I also create a matching trigger. The default version sends on its own.
It is easy to customize a message and not realize it has stopped going to guests.
Request: let a customized system message keep sending on its default event with no extra trigger. At minimum, show a warning when saving ("This message will no longer send automatically unless you create a trigger") and offer a button to create the matching trigger.
Also helpful: let us edit the default subject line, for example action-first ("Payment received · [Property] · [Arrival date]").