You don't need re-registration, registration is done automatically and you are set to vote in a poll station nearby your register address with an official ID.

If you are not citizenship, you don't have an official ID

If your citizenship has expire for one reason or another, you are illegal and thus you don't have a register address, so you don't get a vote registration.

If you change your home address, again, your registration is done automatically for you and you don't need to do anything.

If you can't vote for whatever reason on that day (military, out on a business trip, post-surgery in the hospital...) then you register for mail in voting. Your automatic register is thus automatically deleted and you can only vote by mail in your town city hall with valid official ID. And you need to do it like at least one week before the election so your actual ballot is literally put inside the box that collect the votes before anybody else drop their in person.

These are standard practice through out Europe.