When router changes (in this example from Juniper to Cisco) and interface names change too, the old interface that doesn't exist in that same name in new router(*), still shows in device's interface list, but it shows as status "unknown". When I go to "list resources" page, I can see new interfaces but not the old ones. So I cannot remove it at all!
Of course there is option to delete device and let discovery find it again, but that's not what I want to do, because I have 5 year old data from old device interfaces.
* if Juniper changes to Juniper, then both have same type of interface name for example "FastEthernet0 - Fa0". But Cisco uses type "FastEthernet1/0/2 - Fa1/0/2" so Orion cannot replace interfaces automatically with new routers interfaces.