In the dark ages, some pilots would regularly flash thei landing lights ON when an approaching aircraft was seen.
Some person in a position of authority decided that the lights would be subjected to 'Thermal Shock' if switched on at -45C.
It entered the Ops manual and became SOPs not to do such a thing.
When it was pointed out to him that the filament reaches a temp of 3000C (three thousand) then the starting temp variation from +25 to -45C seems particularly insignificant.
The same can be said of modern Jet engines.
It's a myth.
btw, deleting CLB 1 or CLB 2 will reduce the fuel consumption so very soon you will all be doing it when selecting UP speed or flap retraction.
Bean counters rule.