Switch from a non-cracked server to a cracked one

There's a server that other people has made a lot of progress in, and I can't access it because I have cracked Minecraft. So I want to turn the 'Cracked' option on. But I'm kinda worried that there'll be something wrong with the progress or the inventory of players or anything like that. So should I be concerned? Is there anything I can do to prevent these problems? Is making a backup of the world enough?