Originally Posted by
twospoons
For the most part, once you've completed a goal to unlock a decor item, it stays unlocked so you can purchase more whenever you'd like.
The exception is when S8 chooses to remove items from the marketplace, then you keep the ones you actually own, but cannot purchase more. There's no way to predict if they will remove a specific item like the wedding decor before next christmas or any time, but they do put a timer on it for a few days before it gets removed, so you'll know you should buy it then. But it will not re-lock, so no worries about that.