What failures are you trying to solve? Your 'solution' here is simply assigning an IP address, but this seems specific to only certain types of problems. What is the problem you encountered?
This is a very bad idea, and won't even work anyway.
The Pi's default configuration has the lan on the ethernet port (wifi disabled). OpenWrt uses a default address of 192.168.1.1, and the DHCP server is enabled on the lan. This means the following:
connecting OpenWrt to an existing router/network would likely result in 2 DHCP servers running at the same time (bad)
It would also potentially conflict with the upstream router's IP address (many routers use the same 192.168.1.1 address)
The Pi will not be issued an address because the lan is set to protocol 'static' by default. (not DHCP client)
Moving on, the static address assignment method as recommended in step 4 will likely be within the DHCP pool of the upstream network. This is to be avoided because it is possible that the upstream DHCP server could assign this IP to another device unless it has been 'reserved' on that DHCP server (in which case, there is no reason to statically assign it on OpenWrt).
There are many ways to configure OpenWrt, but I'd recommend avoiding the OP's recommendations.
With no problem statement, it is not clear what the OP is trying to solve. But this procedure is not going to work and may well cause more problems than it solves.