I was able to implement a secondary ipv4 address by sshing into the router as follows:
ifconfig br-lan:1 192.0.2.56 netmask 255.255.255.0
ifconfig br-lan:1 192.0.2.56 netmask 255.255.255.0 up
I did this because setting this address from luci always results in me having to reset and reconfigure.
How do I set the 192.0.2.56 address as either the primary address and not have to reset or make the subinterface "stick"?
what file can I edit?
192.0.2.56/24 is not a private IP range (not rfc1918) and shouldn't be used for those purposes. In principle this would be a case for alias interfaces, similar to the modem access described in the wiki.
Yeah, I'm aware that 192.0.2/24 is supposed to be used only in documentation and is not rfc1918.
That said, for historical reasons this network has been running that block for better than 20 years behind a NAT and is a MAJOR PITA to re-number.
With that bike shed silliness out of the way, what do I edit to make it "sticky" through re-boots?
You add 20 interfaces on physical device, kind of like wan and wan6 are set by default.