The letter says "customers will be automatically transitioned to the new charging (EV2-A) rate plan."
You have no choice and may not remain on EV-A beyond that date. There is some extra grandfathering for NEM solar customers. Those customers will be given at least 5 years from when they started the EV-A plan.
Personally, I'm hoping that I can get 5 years from when I got Powerwalls because I started on the EV-A plan more than 5 years ago and haven't received the letter yet.
If you don't have solar, it won't be that bad on the new plan. There are fewer hours of Peak and the Peak is slightly less expensive ($0.47 vs $0.52/kWh). However, Off-Peak is slightly more expensive at ~$0.15/kWh vs. ~$0.13/kWh for EV-A.