The pro-rated CPD Adjustment will take affect immediately and the new requirement will be displayed on the CPD Portlet for the User:
In the above image, the User has completed 8 hours of CPD and their overall requirement has been reduced from 15 hours to 10, so the 'donut' shows as almost complete.
The CPD Log will also display the new requirement:
Above the Current Status gauge, a note will show that this is a CPD Adjustment. If the User clicks on the link, the reason for the Adjustment will be displayed.