Do not assume the existing authorization covers the changed work. Obtain assessment of the duties and required immigration procedure before relying on the new assignment.
Treat the proposed start as a dependency to resolve
Identify what remains unchanged and what would begin on the new date. Preserve the employer’s written proposal and the most recent authorization record. An internal intention to amend or renew is not a completed immigration step. The appropriate process depends on the actual change; no universal rule makes every revision either automatically covered or necessarily a new application.
Before travel or productive activity, obtain the final duty allocation, confirm the US or foreign employer, the U.S. entity for which the activity will be performed, and the temporary engagement, and match the work to one listed USMCA profession and its qualification rule. Obtain the final employer letter only after the role, supervisor, pay, location, and expected duration are settled; then check whether the degree, licence, and citizenship documents still match that version. Because admission is decided on arrival and the period granted is tied to the employment described, applying against a schedule that has not settled produces either a refusal or an authorization that no longer matches the work.