I want to know if there is a way to copy all non OS settings (i.e. just the full network configs) between routers of different brands.
I know that there would be issues with one router maybe having radio1 and second router having radio 2 etc but I was hoping I could tidy that up, then backup again.
I have tried copying the text out of individual files in /etc/config from one to the other but there seems to be something else required
I guess the big question is if I do this will I break anything?
Worst case, you'll get locked out, especially if it has to do with the network.
For the rest, they should work as long as the interface names are the same in both old and new router.
Personally I would configure the new router from scratch, however you might want to take the risk and download the backup tar, expand it on your PC, then make the corrections, upload it back, cross fingers and restore it.
The chances for the restored settings to actually work on a different device are close to zero.
At least wireless device paths, network/ switch setup, MAC addresses and LED/ GPIO settings are going to be different - almost always (and this list is far from complete).