[eluser]OverZealous[/eluser] @NachoF
I'm not sure what you are asking. The error message is based on the rule. There is a different message for each rule. They cannot (practically) be overridden.
If you want to display a single, generic error message, then you should detect that an error has occurred and render whatever error you want.
Alternatively, write custom _required and _valid_email validation rules for that model, and return the error message you want if an error occurs.