How about this:
Sandbox Mode becomes available on the main menu after you unlock Muerta during the main campaign. You unlock the jungle cosmetic by reaching 5 stars on Matanceros and Nublar by reaching 4 stars on Sorna. This new Nublar is just like the 5 Deaths with a starting budget, division contracts and missions as well as new unlocks, and default dinosaur lifespans, resistance, aggression, and social and environmental needs that can only be modified in the lab. I assume the weather’s nice most of the time, but then you get a bad storm once in awhile. The content in Sandbox Mode equals the content you unlocked during the main campaign, Wu and Claire’s campaigns, and the Challenge Modes on different islands plus much more control freedom obviously. Sandbox Mode also has a map to let you choose where you do what you want. These parks will always be the same as you left them by autosave. Of course, you can always put a park in your save file just before restarting to have many different versions at once.