To the end-user modems, or to the cabinets?
I don't think there is anything needed at all within the modems: they are already capable of the 17MHz frequencies and the new 9098 bandplan - and they just get given the setup during negotiation with the cabinet.
No idea about the cabinets themselves though. The changes involve an update to the way the frequencies are used, as well as the top-end frequency, and the power levels for the transmitter. They will also require new "power mask" settings, to ensure the VDSL signals don't interfere with the existing ADSL/ADSL2+ subscribers.
The Ofcom document that allows this is called the ANFP, and that seems to describe these things in terms of a MIB - which suggests that the cabinets are already capable of the 17a profile, and just need configuring using some SNMP O&M commands.
My cabinet seemed to change around 2AM on a Monday morning, so I guess it isn't a manual visit