Challanges

Bronwin2

From time to time we have these challenges--like the Day of the Dead sugar skulls and that wall shelf. Once the challenge is over we are left with that now permanently locked junk. Is there a way to either get rid of it or unlock it so we can use it?

Cement

You can always sell the items to get rid of them. Using the cheat bb.ignoregameplayunlocksentitlement should unlock the items from prior event challenges, such as the Easter reward bunny and growfruit planter.
To obtain items like the sugar skulls and the eggs, you would have to use bb.showhiddenobjects to find them in build mode.