GL-A1300 - How to disable DFS validation?

Is there a guide to setting the country codes in GL-A1300?
I’ve tinkered with /etc/config/wireless / uci commands to try setting the region, but it seems that the repeater mode is still blocking it.

It’s not that I want to broadcast on DFS channels with the GL-A1300, just to connect it to a DFS channel to be able to use as source internet connection.
I’m guessing that the issue is that the GL-A1300 only has two wireless network interfaces (2.4GHz, 5GHz), which might mean that the 5GHz repeater BSSID needs to be on the same as the AP channel.

If I could just connect to a DFS network, but rebroadcast on any other channels, that works for me too.

A stupid workaround I’ve found is to connect my android phone to the GL-A1300, which has no issues connecting to the DFS channel (of course), and have GL-A1300 use that as the internet source, via USB tethering.

Maybe there’s a way to use another usb wifi adapter to achieve the same without too much tinkering with openwrt?