Obtaining administrator access on Huawei HG8247H

My ISP upgraded my connection from VDSL to fiber and gave me new hardware to go with it – the Huawei HG8247H GPON. However, as I am already using a fully configured DDWRT-ed router for all my networking tasks, I needed to turn the Huawei into a media converter and pass the static IP to my second router – not the easiest task as it appears.

The Huawei my ISP uses comes with manufacturer firmware and blank configuration so the default logins of still work, but as soon as its WAN gets connected it grabs the configuration from the ISP and the administrator login changes.