2.4Ghz band

Yes, this may be possible.  It is both a hardware and firmware issue.    It is a driver written in 'c' that needs updated, then probably some UI code to properly show the channels in a few places.   However, it is unknown how far down the hardware will go before the signal power drops (rec and xmit) getting outside any hardware filters.    Some testing with a spectrum scope would give confidence of the signal quality to make the changes.   

Let's get the issue entered in http://github.com/aredn/aredn_ar71xx .   We're all working on the upgrade to openwrt 19.07 release candidate right now, but if this will help across the pond, we can look at getting it in later.

Joe AE6XE