Review concrete proposed changes before beginning work in reliance on the old arrangement.
Use actual effective dates
Provide the changed duties and current records. An employer’s transition calendar does not itself amend immigration permission.
Set a milestone for receiving the second employer's complete duty letter, a separate milestone for the compatibility review against the first role, and a final milestone for confirming authorization before work starts. Work backwards from the date the employer needs someone in place, and allow time for the support letter to be drafted, reviewed and corrected, which is usually the slowest step. If the start date shifts or the employer changes the role, some preparation may need redoing, and agreeing in advance what a change costs is easier than negotiating mid-file. Keep the employer informed about timing in general terms so start dates and travel plans stay adjustable while arrangements are confirmed. Before new duties begin, decide whether updated admission is appropriate or whether the employer should use Form I-129; a Canadian can otherwise request TN classification at entry. Ask the employer when the revised duties begin, identify what must be resolved beforehand and keep the start flexible until the relevant assessment is complete.