Yeah. On the ASUS DSL-AC68U for example, via a tool called TC, I can actually override the maximum downstream sync rate, INP and delay configuration (even beyond the maximum sync rate set on the DSLAM). So for example, if the DSLAM only permits me a maximum downstream sync rate of 49,000Kbps and I pay for up to 80,000Kbps, I can instruct the ASUS to ignore the PMS from the DSLAM (for the downstream that is) and specify a maximum downstream sync rate of 80,000Kbps (or higher, though I wouldn't) - and this works.
As for SNRM, I don't think G.INP effects that. If anything it allows you to get a higher SNRM because it's not constantly running the overheads imposed by traditional interleaving and INP.