If you are in a user-generated league, it might or might not work, depending on whether the admin does customizations.
In a custom league, it will always work.
In a regular league, it will never work.
Customizations are only allowed before the pre-season. At that time, a "Customize" button will appear on your Team Home Page, underneath future draft picks. Then you will get a menu of how many credits to spend to rename your players, move your team, change your colors, etc., etc.
