I don't think changing the blanket can be done because it can not go to the dresser to enter into CAS mode where style and color can be changed. I tried this before just out of pure curiosity and even when my older Sim carried the baby to the dresser, I couldn't get the baby into CAS mode because they would have to be able to open the drawers. I don't know of any cheats that would help either. It would be cool though to be able to make custom baby blankets. It would allow us an opportunity to do something more fun with our Sim babies than just taking care of their needs. Sorry that I couldn't offer any new help, but I do share your thoughts about this.