The only way to do this is with the reset slot button in the load menu. You can choose what to reset, but you'll need to reset events and objects for the most new content.
I advise you use the mailbox to send your precious plushies, engraved golden rings and warehouse full of shrimp to a temporary save, along with anything else you might want. Just remember that containers you put in there will be emptied!
Then you can safely reset events and objects, load it up, and keep your loot. BUT if you're far along the story, this might not be the best experience for you. Your Mileage May Vary!