cascadingDeletion is an attribute of Relationship Type element. If developers define a Relationship Type with cascadingDeletion setting to "no", then they want to reuse this Relationship Type but they want cascadingDeletion with the value of "yes". There is no place for developers to reset this attribute in Relationship Template. They have to define a new Relationship Type with cascadingDeletion setting to "yes" and no change to all other properties.