CityFibre change the VLANs your ONU maps to on their equipment and you end up being switched to the new ISP. That's all there is to it from their point of view, VLAN changes.

PPP is nothing to do with CityFibre, they send your data to the ISP in the same way whether it's there or not.

Thanks for your reply.
All makes sense now, think that answers all my questions haha!

In reply to a post by 0007:

In reply to a post by XGS_Is_On:

On how some ISPs manage to offer wires only most don't. Even in the USA where people are used to bringing their own cable modems they require use of their own ONUs.

Thanks for your reply, and yeah I've noticed most don't.
Originally I just wanted to first know if it was possible.
Now I know it's not possible, it's more of a why wouldn't the ISP allow for it. A number of issues have been mentioned in terms of why they don't allow for it. But then I can't see why other large ISP's in other countries have managed to get away with letting customers use their own SFP Transceiver.

It is very much possible.
Here you will find some useful info how to actaully do it:

https://akeyx.github.io/blog/ont-hacking/
https://chochol.io/en/computer-networking/how-to-con...