Sex and the Census request that you still register your objections with the letter.
From their website
"Do I still need to register an objection now that FPFW have won their legal action against the ONS?
Yes. We still want you to do this.
The legal victory by FOFW is hugely significant: the guidance by ONS that said you could self-identify your sex has been withdrawn. Now you must answer the sex question with reference to your legal sex (birth certificate or GRC).
This is a big step forward. The Courts have determined that sex cannot be self-identified and this will mean that other public bodies and organisations will follow suit.
But we believe the sex question should actually be answered on the basis of biological, not legal, sex. That’s why we are still asking you to register your objections to the collection of inaccurate sex data by ordering a paper copy and enclose our template letter."