When training for an event, you will likely gain fitness. Your auto-calculated Critical Power will automatically adjust, and if you prefer a manual test, it is recommended to repeat your Critical Power test every 4 to 6 weeks.
If you update your Critical Power, your power-based training plan does not change at all (whether you use a Stryd power training plan within PowerCenter or any other power-based plan). What does change are your Power Zones. Since your zones will shift, you will have to run harder during your training runs to hit the right zones.