I don't know how the ATR powerplant works, but on the turboprop engine I'm most familiar with, if you have a loss of engine power, pulling the throttle back to flight idle will have no effect on prop pitch, and thus no effect on drag.
If you've lost engine torque, and the prop hasn't been feathered by an auto-feather system, in most cases the prop will *already* have been driven to the low pitch stops by the governor in an effort to maintain prop RPM. At that point pulling the throttle lever back won't change the prop setting.
Does the ATR powerplant do something substantially different than this?