The ATR 42 FCOM states that the engine #1 is to be started during taxi, also in the procedures and techniques chapter were Normal taxi is despicted that there "is NO limitations to go either forward or rearward", it even recommends that the starting of the engine could be performed while taxi is in progress being cautioned to do it where the workload is low enough to monitor it efficiently.
Even in adverse wheather it could be done, by SOP means, when the taxiways are not icy or with slush, but if the OAT is to low you should warm up the engine before take off.
Also when taxi-in, the engine #1 could be stopped allowing at least 1 min. cooling time.
Remember that the ATR does not have an APU and engine #2 has a propeller brake that once engaged on the ground serves as an APU.
In regional airports where taxi-in and taxi-out times are very short this procedure turn out to be time and attention consuming, so normally no operator does it unless there are expected delays of 10 minutes or more while taxiing