Is there a way to change the state of a template sensor from a custom card?

I have created this birthday reminder custom card for Lovelace: Birthday reminder card for Lovelace
It works as planned, but it only displays the reminders in the Lovelace UI. I would like to add an option to launch a notify action (for example to the iOS app) with a list of birthdays that occurs “today” (with an option to set the time for these messages to be sent, to avoid waking up people in the middle of the night).

My thought was to create a template sensor, and set the state of this sensor from the custom card, and then use an automation to send the notify message when this sensor changes from ‘off’. And to set the template sensor to ‘off’ again for days without birthdays. But - I haven’t discovered a way to do this. Does anyone know if this would be possible?

Or the other way around - could a template sensor mirror a variable created by the card, containing the birthdays for today?

Or is there a way to send a notify action directly from the custom card?

Any other ideas?