The first stage of the proposed changes to the Domestic Renewable Heat Incentive come into effect on 20th September 2017, subject to Parliamentary approval.
The changes which already came into effect on 31st July 2017 were the MCS standard updates. The Stage 1 changes which will come into effect on 20th September 2017 are the Tariff uplift and Heat demand limits.
Stage 2 amendments of Metering for Performance, Metering and Monitoring Service Package (MMSP) payment & sanctions and Assignment of Rights are likely to follow later in 2017/2018, subject to Parliamentary approval.
For full details on the amendments and changes see the Ofgem Domestic RHI factsheet here