On a command line aka Terminal, go for:
ssh root@gl-ar300m-xyz
Replace xyz with the last three characters of your MAC or simply use the SSID printed on the back of your GL.iNet – the ‘hostname’ of your GL.iNet. Then, you go for
uci set wireless.@wifi-iface[0].ssid='your SSID'
uci commit wireless
wifi
More settings and real-life example in this thread …
When you change via Web → More → Network Mode to Access Point, you are able to access your GL.iNet from your usual home network, your main router directly. Therefore, with that, you could disable the Wi-Fi in the GL.iNet.
When you keep the Network Mode as Router but add a Port Forwarding for TCP port 80, you are able to access your GL.iNet from your usual home network, your main router directly. Therefore, with that, you could disable the Wi-Fi in the GL.iNet.
However, that is a second-class alternative. I recommend to change the Network Mode to Access Point as describe before – it even should make your GL.iNet a bit faster, because all that unneeded Firewall and Masquerading services are not running anymore.
I still wonder why you cannot change the SSID via the GL.iNet interfaces. Here with my GL-AR300M16, I go for 192.168.8.1 → Wireless → (tab) 2.4G Wi-Fi → (button) Modify. Are you using not the Web but the App interface? Never tried the GL.iNet app.
If your computer uses the DNS proxy of your router, go for a Web browser, and enter the SSID printed on the back of your GL.iNet – its ‘hostname’ – in your case it sounds to be http://gl-ar300m-408
That way, you do not have to find the IP address.
Yes, that is the alternative to UCI (and LuCI, and the GL.iNet Web UI). Glad you made it.
If you cannot wait/stand it, I recommend to have a look at the latest GL-AR300M series. They come with an additional NAND flash. Perhaps the GL.iNet support is able to confirm that, but I think you can use that for additional space for software packages. One of the benefits of GL.iNet routers are their bigger ram/storage compared to other off-the shelf routers because OpenWrt itself is known to be hungry.