At minimum, a support letter describing the position as it now stands: the professional title, the specific duties, the reporting relationship, the employer entity, and the expected duration. Keep the superseded version as well, so the change is documented rather than looking like an inconsistency.
Keep both versions, dated
An officer or reviewer comparing documents will notice differences between an earlier draft and a later one. Having both, with dates and a plain explanation of the reorganization, is far better than a single revised letter that quietly contradicts something already submitted or presented. Ask the employer to describe duties concretely rather than with departmental language that only makes sense internally.
Start by matching the passport, legal-name evidence, diploma, transcript and employer letter, then test the substance separately. The complete TN package must still prove citizenship, a prearranged professional engagement, a listed USMCA occupation, and the category-specific qualification. The first review should make a document-to-claim list: passport for citizenship, credential evidence for the professional listing, and the agreement for duties, place, payor, and end date. Obtain translations or evaluations early when needed; a late correction can make the employer letter inconsistent with the credentials.