[quote]Can they even do this?[/quote]
Clearly they can if they did lol. Whether or not it's right is another thing. Which leaderboard is it? Rule changes can occur in response to new runs if the changes make sense and it's not just being done to protect records.

Speedrunning

Can a moderator change rules without giving any reason?

Pixel Rooms 2

Pixel Rooms 1

King of Thieves

Blu Escape

Nameless Cat

Tap Tap Speedrun

Mangavania: Action Platformer

Candies 'n Curses

OBSOLETE

Hexoboy

Lucky Luna

Escape The Dungeon

Song of Bloom

Jwnee