CET import multiple substations

In 800xA release 5.1 it was possible to import multiple substation scd files in CET after each other. In release 6.0 that has changed which causes the present substation to be replaced by the loaded one. For this I made a support case but it is claimed to be like this by design and that the 5.1 method was faulty. Merging scd files in IET600 is not possible. The easiest way is the 5.1 method but do you know how to achieve that?