I can confirm that ADSL2 DLM can be 'turned off' via a cooperative and understanding ISP.......mine was done so back in 2014 and remained off until I moved to FTTC in 2015. The absence of DLM benefitted my line enormously.
For years my line experienced huge CRC error rates at times during spring-autumn - sporadically, sometimes for weeks at a time, but stopping during rain. The high rates caused DLM to hit my line with very high interleaving and increased SNRM, neither of which reduced the high CRCs. It wasn't until 2014 that I was able to accurately pinpoint the cause - it was electric fences several hundred yards away. The farmer allowed me to confirm the cause, by temporarily turning a fence off, and seeing the CRCs immediately cease, but I could not expect him to undertake expensive problem rectification. An extremely helpful agent at my ISP (sorry, I agreed not to specify them) tried various measures over a period of a couple of weeks, but none caused any CRC reduction, and eventually he agreed to place an order with BTW to 'turn off' DLM - I don't know what the exact terminology was. The result, as intended, was that the high CRCs continued, but DLM didn't then take any annoying action. It proved a good work-round for 12 months till fibre arrived.
When fibre was initially activated, I could still see the high fence-induced CRCs, but within 24 hours, VDSL DLM applied interleaving and G.INP which dealt with them, reducing CRCs and ES to almost zero. FECs increased, but didn't affect my VDSL experience.
