It's not possible to get a widget by its Id since in platform widgets are not objects (they have records, but you can't assing it to a variable for example).
However, you can achieve this by javascript. You could get the widgets elements at clientside (find by a extended property that identifies it) and change the associated Validation Message. It will demand some work, but it is possible.
Hope it helps.
However, you can achieve this by javascript. You could get the widgets elements at clientside (find by a extended property that identifies it) and change the associated Validation Message. It will demand some work, but it is possible.
Hope it helps.