I tested the Sim Manipulator in Castaway Stories (After the story was completed) and it works fine.

Once you had finished Riley's and Vincent's stories you can't use their respective story rewards with each other. Vincent and the sims in his neighborhood can't use Riley's story rewards (Except the coffeee maker in my playthrought for some reason) and Riley and the other sims in her neighborhood can't use Vincent's cool story rewards like the computer, electric guitar and pool table.
There's a way to unlock them for all the sims using SimPE?

https://db.modthesims.info/showthread.php?p=5901224#post5901224
According to this post the Story Rewards lock status is stored in the NeighborhoodManager.package for Castaway Stories, it's very much likely the same for SLS, but I don't know exactly where it is inside the package file. It would be great if someone points out where to look out for it.