I have one AC68U (router mode) running firewall, Diversion, Skynet, and DNSCrypt. This feeds a Ubiquity ER-X and splits into two subnets (home and surveillance). There are two AC68U's (ap mode) set up for the appropriate subnets, and each of these is daisy-chained to one or more AC68U's (ap mode). One subnet uses Windows AD for DNS/DHCP for the whole shebang.
I have found that the easiest thing to do is to go to each subnet's first router User Map and click on the Clients button, then, on the right side you can edit each clients icon and name.
Nest, ssh into the router and type/enter:
nvram get custom_clientlist
This can be copied to a text file where it can be edited and/or saved for later use. Whenever you do a Factory or NVRAM reset, just ssh into the router and type/enter:
nvram set custom_clientlist="paste text from saved file here"
The clientlist is formatted as <name>mac address>0>icon#>><name2>mac address2>0>icon#>>...
I have three of these files: one for the firewall, a second for one of the subnets and a third for the other subnet. The respective data gets pasted into each appropriate router so that useful names show up in Network Map/Clients, Network Map/List and AiMesh Client List.
This just basically shows the name in the lists, it don't know that it will have any impact on dnsmasq DNS/DHCP.