Forcing or disallowing certain adsl/vdsl profiles

I'm interested in using openwrt for an unusual application for VDSL, I have a coaxial cable on a winch which can vary in impedance. When the impedance increases the vdsl modems have to renegotiate which takes a lot of time.

I would like to know if it's possible to force using 8a/b/c/d or 12a/b to limit the frequency used to make the line more stable? I've seen it's possible on the technicolor flavour of openwrt with uci del_list xdsl.dsl0.profile='NNn' but I've searched extensively and haven't been able to find if it's possible with the lantiq or intel vdsl controllers.

On the other end, I will have an SFP CO proscend modem andI'm not even sure they will work together at all.

Are there any other ways to limit the frequency of the vdsl controller, bar using a low pass filter?

I only need 1-2mbps so profile 8 or 12 would be perfect for me, as long as the line is stable.

Thanks for any replies!