Set empty list and avoid inherited list for the child object


I have a parent object, field of type many-to-many object relation. The object has 2 items set in the field.
With Allow Inheritance set to true, a child object inherits the 2 items on the field.
How can I maintain the data in the parent, but for the child, I set it to an empty list?
At the moment, if i remove the 2 items on the child, save, and reload, it is maintained.