Answer
This depends entirely on where the error originates. If the error is raised from plain PL/SQL or from inside an Event Action, forcing a refresh this way isn't supported — that specific combination simply doesn't have a force-refresh option. But if the error is instead raised from a Custom Menu of PL/SQL Block type, that Custom Menu has its own 'Refresh window after execution' option, which does force the screen's data to refresh once the block finishes executing. So if forcing a refresh alongside a validation message is a genuine requirement, implementing the check as a Custom Menu action, rather than a background Event Action, is the way to get that automatic refresh behavior.