bool IsConverter(IPublishedPropertyType propertyType);

public bool IsConverter(IPublishedPropertyType propertyType)
{
    return propertyType.EditorAlias.Equals("Umbraco.TextBox");
}

IEnterspeedProperty Convert(IPublishedProperty property, string culture);

public IEnterspeedProperty Convert(IPublishedProperty property, string culture)
{
    var value = property.GetValue<string>(culture);
    return new StringEnterspeedProperty(property.Alias, value);
}

public class MyCustomerPropertyValueConverterComposer : IComposer
{
    public void Compose(IUmbracoBuilder builder)
    {
        builder.EnterspeedPropertyValueConverters()
                .Append<MyCustomPropertyValueConverter>();
    }
}

[RuntimeLevel(MinLevel = RuntimeLevel.Run)]
public class MyCustomerPropertyValueConverterComposer : IUserComposer
{
    composition.EnterspeedPropertyValueConverters()
                .Append<MyCustomPropertyValueConverter>();
}

public class RegisterCustomPropertyValueConverters : ApplicationEventHandler
{
    protected override void ApplicationStarted(UmbracoApplicationBase umbracoApplication, ApplicationContext applicationContext)
    {
        EnterspeedContext.Current.EnterspeedPropertyValueConverters
            .Append<MyEmbeddedContentPropertyValueConverter>();
    }
}

[ComposeAfter(typeof(EnterspeedComposer))]
public class MyCustomerPropertyValueConverterComposer : IComposer
{
    public void Compose(IUmbracoBuilder builder)
    {
        builder.EnterspeedPropertyValueConverters()
            .InsertBefore<DefaultTextboxPropertyValueConverter,MyCustomPropertyValueConverter>();
    }
}

[RuntimeLevel(MinLevel = RuntimeLevel.Run)]
public class MyCustomerPropertyValueConverterComposer : IUserComposer
{
    composition.EnterspeedPropertyValueConverters()
    .InsertBefore<DefaultTextboxPropertyValueConverter,MyCustomPropertyValueConverter>();
}

public class RegisterCustomPropertyValueConverters : ApplicationEventHandler
{
    protected override void ApplicationStarted(UmbracoApplicationBase umbracoApplication, ApplicationContext applicationContext)
    {
        EnterspeedContext.Current.EnterspeedPropertyValueConverters
            .InsertBefore<DefaultTextboxPropertyValueConverter, MyCustomTextboxPropertyValueConverter>();
    }
}