It's not possible to modify an "Original" or "Duplicate"-incident to any other relationship type.
And it's not possible to modify an related incident (whatever relationship type) as "Original" or "Duplicate".
So as to change the relationship from "original of" to any other relationship type we need to follow two step process to first un-relate the incident and relate it again with related to type. That's very cumbersome.
--> The possibility to change the relationsship from "Duplicate" to any other relationship type or or the other way round would be very helpful.