AT - NB I am not familiar with trim setting on ALL aircraft types and there may be a few where it is crucial, but in my experience as long as the trim is in the right 'area' there will be little problem with variations in thrust since elevator control is sufficient to compensate for minor differences, hence as Sc says, it does not change (737) for a reduced (assumed) temp - nor does it change for take-off speed incidentally. I never flew a 737 with a fixed derate so I cannot comment but it is possible that a very minor change is present in the published settings tables.
Where did your original quote come from?