Currently whenever the mount point of the MergingResourcePicker (/mnt/overlay) or OverridingResourcePicker (/mnt/override) is used, the merging always takes place. It is only possible to hide/modify individual resource/properties of the underlying resources but not to completely disable the inheritance (and by that replace the whole overriden/overlaid resource).
A concrete usecase for that is in a CMS (e.g. AEM) where the dialog definitions are always loaded via /mnt/override/<resource type>. In that case it is not easily possible to completely replace the dialog of the resource super type (as only individual child resources or properties can be hidden but there is no special property to ignore the inherited resource alltogether).
I propose the following:
Add a new property sling:disregardInheritedResource=true in which case all the inherited resources would not be taken into account for merging.