G'day,
Successfully replaced one of these with a Huawei MA5671A sfp module purchased from Ali Express for .
Details in this post
https://forum.kitz.co.uk/index.php/topic,26900.0.html.
Recently, circa 2023 or after switching ISPs, these are fully locked, no access to web interface. I have tried via the internal serial header on the pcb and seen no login, it all ends with a message that the ONT is up.
I guess that the firmware can be dumped either by desoldering the flash chip or by JTAG interface, but those things cost a bit too much.
Have a read and a go, it's easy.
Best of luck,
m.