How do you change the default IP of the XFi gateway or turn it into a true bridge??

When I upgraded to the XFi gateway, I found that it was basically requiring me to use it as the default gateway.   Prior to that I had been using my Netgear Nighthawk R8000 router flawlessly for DHCP, wireless and LAN connectivity on my network.  

However, the XFi gateway INSISTS on being 192.168.1.1 and will not allow you to change that last octet number.  Fine, I left it alone and changed my Netgear router to .2 and set it up as an AP.

The recent data cap changes mean that I need to use QoS on my network to see which devices are using up data.  Despite Xfinitiy's assurrances, I appear to be one of those that are close to the 5% that are likely to be above the data cap.  Different topic, not sure why.  Our house usage isn't all that different from others.

Regardless, I wanted to turn the XFi gateway back into Bridge mode, set my Netgear to be the default gateway and have QoS features turned on.  

It seems, though, even though I've read that Bridge mode turns OFF that IP, it's not possible to do this.  I turn on Bridge mode and the router status shows it as 192.168.1.1 and the entire section is not editable.   This, obviously, conflicts with my router.

According to: https://www.xfinity.com/support/articles/wireless-gateway-enable-disable-bridge-mode, if I've enabled bridge mode and I want to change it back, I have to connect to the gateway via an ethernet cable.  

How do I know it's not working? Because after setting bridge mode, I'm able to connect to 192.168.1.1 again via a web browser.

Any help here?  

BTW: it's really bogus to enable a data cap and not allow for QoS features to montior usage by device.