A change in tariff classification is an origin criterion satisfied when the finished product is classified under a different Harmonized System code from the non-originating materials used to make it — the processing must have moved the goods across a classification boundary. The strictness depends on which level the rule specifies: a required change of chapter is demanding, a change of heading less so, and a change of subheading less again, since a smaller move is easier to achieve. Rules are often accompanied by exceptions barring a change from particular materials. Classify the inputs and the output correctly first, because everything follows from that.
Why this entry carries no source list. The concept generalises; the definition does not. What this term means for your shipment is set by the particular trade agreement’s own text — its origin protocol, its annexes, its tariff schedules — and two agreements can use the same word differently. There is no central authority to cite, and citing one agreement would imply a generality that does not exist. The operative document is the one governing your trade, and it is what a customs authority will read.