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.
If you have additional questions, contact firstname.lastname@example.org.