No, there's not a way to do this. The Overlay message system is built like a queue, and once a message is dropped into that queue to be displayed, it isn't updated (it's static; non-changing).
But you could do something similar in a number of ways. For example, you could add another Property Group to the Clock cell that only displays once the clock gets below a certain threshold. While the normal clock cell just says:
<clock>
The Property Group you create would say:
**** Blinds Increasing In ****
<clock>
So basically the words "**** Blinds Increasing In ****" get added to the screen when the clock hits that threshold.