How to control additional tethering settings on android phones? I want to use my phone and data plan as a temporary solution for providing Internet for my whole home network. 

I have plugged it into my OpenWRT router via USB and it's network device usb0 is so far member of the bridge br0 so that all my network can use it. All is working fine except for one thing:

The phone now acts as DHCP Server and the subnet (192.168.42.0) is not controllable and different to the previous subnet in my home network (192.168.2.0). I have a few fixed IPs that I don't want to change. 

It would be great if I can change the phone's tethering subnet to be 192.168.2.*.
Is this possible?
Instead of changing the IP of the phone's network, you might simply change your router's config so usb0 is not in the brige any more but is configured more like a "WAN" port, complete with the usual NAT.  In this configuration, the phone's DHCP server will only serve an address to your router (to use for the usb0 interface), and all the router's clients will get their IP from your router instead.

The advantage also is that if/when you want to get your internet access from elsewhere (e.g. DSL/cable/younameit), you'll only need to change this part, but all the local network config will stay the same.