Well,

More than modifying the UI, what I would really like is to build my own openwrt but still have the GLI UI that it ships with.

Since it’s not a kernel module, could I simply install the binary package?

An API to extend it would be useful.

Am I right in assuming that if I build OpenWRT from your patched github it won’t have the GLI UI only the standard Openwrt one?

Good job with the router by the way, the MT300N is a fantastic little device!