It would be nice to be able to edit the list but there are other tools that can be used to scan the LAN and discover devices. If you send a ping to the broadcast address for the network and then display the ARP table of the client the you at least have the IP to MAC address mapping and have a good starting point. With a network scanning utility you can get more information. It also helps to assign friendly host names to clients. It takes a bit of time in some cases but when you are done you know what is where and have what you want. 
 

I do agree the “manage devices” is very lacking as seeing only is not managing.