Assess the new duties and the appropriate process before relying on the earlier professional assignment. The original study does not automatically authorize materially different work.
Record the change in the assignment
Keep the final scientific deliverables and the proposed shift responsibilities distinguishable. Identify whether qualifying professional chemical work remains and what additional duties are intended. A production shortage does not extend status or turn all operating work into the profession previously described. Use the actual immigration record and changed proposal to plan the next step.
Identify the latest date the employer could actually accommodate a delayed start without cancelling the position, and avoid non-refundable travel or equipment commitments tied to an assumed entry date. Once the record is stable, a Canadian outside the United States may request TN classification at a port of entry or the US employer may first file Form I-129; after approval of an advance petition, the Canadian must still seek admission. Where restructuring is required, the limiting factor is usually a board or shareholder approval process with its own meeting calendar, so ask early when the next opportunity to approve a change falls.