So the person you are spoiling decides to block the number. Pretty clever.
In general, it shouldn't matter. The number we send from shuffles.
That said, if they reply "STOP" or "UNSUBSCRIBE" they won't receive any further messages. Telecom companies do that automatically to comply with the law. It usually applies to all messages we send, even if they come from a different number. It's unlikely your friend would receive a "reply stop to unsubscribe" message, but each cellular carrier does things a little differently.
Lastly, we're constantly updating the app. We can't promise it will work the same way tomorrow as it does today.