How can I override a method in the base package

Hi All,

There is a ActivityFile Event Listener is defined a base package and they have defined a validation method in private. Now I have to change that validation as per request.

But I cannot override that method as it is declared private or cannot change the base class definition. what could be done here?

Is there any recommended way to change the base package definition and send the same changes to PROD? 

public class GlbActivityFileEventListener : BaseEntityEventListener
{
 
private bool isNeedValidation(Entity entity){
.....
}
 
public override void OnUpdated(object sender, EntityAfterEventArgs e){
base.OnUpdated(sender, e);
if (isNeedValidation(entity)){
.....
}
}
}