I'm not sure, whether I get your question right, so I'll just try to explain.
Definition: Icing conditions exist when visible moisture is present and the TAT (inflight) or the OAT (on ground) is below +10°C.
ENG A/I must be ON in all phases of flight when Icing-Conditions exist.
No rule without exemption:
During Climb and Cruise with the SAT below -40°C the ENG A/I may be switched OFF, even when visible moisture is present.
Why? The RAM effect caused by the airframe hitting the air at IAS will heat up by as much as 25K at 350 kts IAS. At SATs below -40°C this resulting TATs are well below freezing point (i.e. remain frozen) and thus by definition icing is not possible.
Prior to and during descent in icing conditions the ENG A/I must be ON even at SATs below -40°C.
That's just a precaution, as Engine Speed is at or near flight idle during descent and the engine ist far more vulnerable to icing (which maybe does not know the definition of icing ;-).
Was that what you wanted to know?
Cheers, MAX
Ah, and by the way: Critical System Operation as ENG A/I ist practically done EXACTLY by phrases of the manual.