Change of material spec, change of process it is all change of design to some degree - just depends how you use the word.
Any change untested is very silly and I think had I got my feet wet in G-REDW or G-CHC I'd be with my lawyer seeking damages as it's unforgivable to put onto service something untested.
As an aside since when did we start using total fleet hours as a benchmark for fitness for purpose?? 250k hours could just mean 1 million things lasting 15mins as much as 1 thing lasting 250k hours.. To exaggerate the point.