NEW: There is no same-day voter registration in Mississippi; voters must register 30 days before an election.

But local election officials are free to move polling precincts around—even 13 hours before an election.

And two just moved in Hinds County.
https://www.mississippifreepress.org/35330/hinds-county-moves-two-polling-places-hours-before-polls-open

Hinds County Moves Two Polling Places Hours Before Polls Open

Just shy of 6 p.m. Monday, Hinds County officials announced that they were moving two precincts just over 13 hours before polls open.

Mississippi Free Press
@ashton As someone who has worked extensively in elections administration in California: this is a difficult area because sometimes issues come up that make it necessary and prudent to move polling sites, sometimes even at the last minute, but that kind of (any kind of) discretion, while necessary, can also be abused by administrators with less than noble motives. Any kind of human endeavor is also vulnerable to human failings and mischief.