All FTTC lines are currently maintained by BT OpenReach.
The DSLAM is theirs and the DLM is run by them. No ISP can currently override this.
Lowering the SNR is generally a "bad" idea on FTTC as the instability potentially caused will almost certainly trigger DLM.
Since cross talk will almost invariably be the limiting factor on you line's performance there "may be" nothing to gain.
I would think that the only way to "bodge" the SNR is currently with a FritzBox?
BT Infinity 2 - IP profile 77 / 20 - super fast!
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