Suggested implementation:
After each change to exhibition config or exhibition config visibility save the information to the database using a uniqueId based on the pid and indicating that it's a draft (ex: draft_si:1234 as the pid)
Remove the draft from the database when the config is saved.

When loading exhibition config, load up the draft version if it exists. Give an indication that what they are viewing is NOT what is currently saved. Drupal usually does this with a yellow warning that is visible on the same screen as the changes are happening, so follow that convention.

On the UI, show a "revert to last save" button (wording can be different, "discard draft", etc whatever may be most understandable), which would give a confirmation dialog and if confirmed, delete the draft and reload from the saved version of the config.