Depends on the router model.

I have had good success repurposing an unused PLDT ONU (HG6245D) as an AP to cover my garage and workshop. Though I had to go through several steps, both inside the web interface and telnet (CLI) to set it up to my liking. It's not completely de-branded but at least it no longer "calls home".

This unit does not have mesh or repeater capabilities. It needs to be connected to your wired LAN.