Attributes overrides is already available in Skipper. Associations overrides isn't implemented yet.
Unfortunately whole override mechanism is very messy and it's not easy to implement it because of it's nature. Because of low demand of this feature (you're the first one) we have this feature on the bottom of our todo list so I can't promise any specific term.
From our point of view it's better to avoid these two features (attributes and associations override) because using it isn't a good and clean way how to create your models.