Can a medical exam result be reassessed if my health changes before I land in Canada?

Yes, and in some cases it has to be. Immigration medical exams have a limited period of validity, and if there's a meaningful change in health — for better or worse — before someone actually becomes a permanent resident or is otherwise admitted, that change can be relevant, and a new or updated assessment may be required rather than optional.

If a condition develops or worsens after the original exam, disclosing it rather than staying quiet matters: proceeding on an exam that no longer reflects reality can itself create a misrepresentation problem, separate from whatever the health issue is on its own. On the other hand, if a condition improves or resolves, that can genuinely help an applicant who was facing, or worried about, an excessive demand concern, since the assessment is meant to reflect the person's actual anticipated needs, not a fixed determination made once and never revisited.

Because exam validity periods and the process for updating results have specific requirements, anyone whose health changes meaningfully during a pending application should raise it proactively with their representative rather than waiting to see whether it's noticed, especially as the application moves closer to a final decision.