IM (as of V8.3b) allows a property that is a redefinition to have its type changed to a type that exists in the type hierarchy of the properties base type (i.e. before it was redefined). The type picker for a redefined property only shows the sub-types that are available based on the properties current type. This means the type picker cannot be used to change the redefinition from a specific type to a more general type as far back as its base type in the type hierarchy. The means that once a sub-type has been selected for the redefinition that it cannot be undone or another type at the same level in the type hierarchy selected. Please add this feature.
Sometimes, deleting the redefinition and starting again with a new redefinition provides an adequate workaround. However, when a property is present on an IBD the redefinition is often related to other items that will be lost when it is deleted. This further complicated by the use of virtual redefinitions on IBDs, because deleting a redefinition does not result in it being replaced by a virtual redefinition in the IBD.
Also note that redefined properties can be inherited and then subsequently redefined. Need to consider (i.e. check the UML standard) whether the type picker should work with the properties original base type or be constrained to start with the inherited properties type as its current base type.