If I change my new routers default IPv4 address on my new router to the IPv4 address on my last router, will my network completely fall apart or is it straight forward? I only want to change it...

I'm trying to setup my AC1200 but seem to be failing at every turn. The QR code isn't recognised, the 2.5Ghz and 5Ghz signals are there but I cannot connect to either? So, until I can connect to the...