Do you know how to override property value in edit mode?

For example:

public virtual string AboutUsLinksTitle
{
      get
      {
           var value = this.GetPropertyValue(p => p.AboutUsLinksTitle);
           return string.IsNullOrWhiteSpace(value) ? "overrided value" : value;
      }
      set
      {
           this.SetPropertyValue(p => p.AboutUsLinksTitle, value);
      }
}

In debug it returns "overrided value", but shows empty value. It's probably, because of proxy class which is created in the background...

Thanks!