Not possible since it is standard behavior of this data-type. A bit cumbersome, but you can create another entity-attribute of type string and pass the value into that one, do your check and if ok, pass it on. But that is too much trouble for little gain.
You can update the validation message from the System texts under the project module.
And you can create a custom validation by adding an On change event on the text field to call a Microflow or Nanoflow, and add the regex on a decision and the message can be added into a validation feedback action activity.