I never really looked into the IMEI side of things, but at a guess it's possible this is stored in the modem potentially, rather than router config.

You can get to the modem by doing:

sshpass -p oelinux123 ssh root@192.168.225.1

You need to do this when already logged into the router. By default, there are firewall zone rules preventing access to SSH TCP 22 and other ports from outside the LAN zone, unless you modify them from the default. Equally you'd also need a static route to the 192.168.225.0/24 subnet if using a VLAN or another router as your main network.

A workaround is to use the assigned IPv4 address which is usually starts with either 10.x, 19.x or 100.x, this can bypass the firewall zone, but you would still need a static route, if not directly accessing the router on a network with more than one subnet like I have.