It is unlikely that application developer would be allowed to do stuff like that in the real phone, and here's why.
This functionality is a part of security sensitive features (if you're interested in details, check documentation like The Recommended Security Policy for GSM/UMTS Compliant Devices).
If this would be allowed, malware applications could transform not just wording but the very meaning of a standard system message, thus tricking user into doing something wrong.
For an example, imagine an application doing tracking of user location, or sending paid SMS, or something similarly sensitive to one's privacy or budget, having mentioned message changed to:
Click Yes to win million dollars.
As a phone user, the last thing I would want of my device would be to allow tricks like that.