Never received any help on the case created on Support site so went ahead and solved it myself.
Was able to "deassociate" storage systems with old host service. Then all objects related to old storage service was marked deleted in database. In the dataset I replaced the deleted object with the new ones. Then its was possible to delete the old host service.
Will try the 'dfm hs unregister -f' next time I need to move the host service if NetApp hasn't made a guide for it then.