Deleting icloud.com mail account from single user on multiple user computer
When you delete an iCloud account from OS X system preferences, nothing changes on Apple's server side. No data is lost, just your local copy is removed and the syncing stops.


Sign out in one or all accounts
Sign back in on the Mac account where you want to use iCloud


No matter what I say, a Time Machine backup before starting any change is always a good thing, just in I wasn't clear to you or something goes wrong or I'm wrong.