With this command, you will be prompted with a list of all updates to be applied and a prompt as to whether you want to proceed (y/N).
'urpmi --auto-select' will find all newer packages from all your configured sources (main, contrib,updates, non-free, free, plf, backports (if you've enabled it, etc etc). To be sure the hdlists are up-to-date, you could do an 'urpmi.update -a' first. Check that you've got all the repositories with easy-urpmi.
If you just want those new packages from the updates repositories, you would use the command: 'urpmi --update --auto-select'
Yes, the plf versions of mandriva packages typically (always?) will have a version number such that it will replace the base mandriva package.
Is it safe to do so? Always check the list before proceeding. Also, you could always use the MCC packages tool. Make sure you know what repositories are configured and that you have all of them (there are a lot of new ones with recent Mandriva versions). Easy-urpmi is your friend.
Also, see this excellent thread started by the brilliant arctic:
https://mandrivausers.org/index.php?showtopic=40552&hl=