Establish default value for an overwrite page property

I have a property called subtitle in a base page and would like to overwrite this property with a default value. What I'm trying is to do the following, but the field do not appear in the CMS

public override string SubTitle => ServiceLocator.Current.GetInstance<LocalizationProvider>().GetString(() => PageResources.Vacancy.Subtitle);

Is there anyway to do that?

I'm running EpiServer 10.10.4