Any new objects saved on the Front-End will remain in the Front-End and should not affect the Back-End. They will only be available to that specific Front-End (if each user has their own Front-End, no one else will see it).
However, the thing to consider is updates to the Front-End. If a new Front-End is distributed, it will replace the existing one, so any customizations to a singular Front-End would probably be lost at that point.