We recommend that under 'Notifications' in your TrainingPeaks settings you choose 'Notify me of suggested threshold changes vis email' and leave 'Automatically apply new threshold changes' unchecked.
TrainingPeaks will then send you a notification. However, this is only a suggestion.
You can then consider the suggested change and if it feels correct, go ahead and update your threshold and recalculate your 5 personalised MyProCoach training zones. If it doesn't feel right then leave your settings as they are.