1. Plan to finish two weeks early: vendors often start degrading before the announced date
2. Change one system at a time and keep the old path until the new one has served real traffic
3. Test the failure, not only the success: expired keys, rate limits and the error format can change too
4. After the date passes, confirm in production logs that nothing still calls the old path
5. Set Status to Done and note the release in What changes for us