Problem: Once your baby sees her Halloween costume, she's not going to want to wear anything else. Ever. You don't want her to eat or sleep in it; you don't want parts lost or stained. But it will be very difficult to save the costume for Halloween, itself. Especially if your child goes to daycare or preschool. They probably have already worn it at some party or parade.
Solution: Tell your baby you need to wash the costume, and you'll give it right back to them. This works especially well if they are about to take a bath or a nap. I find if I can calmly explain to my kids that something needs to be washed, they give it up in trust that they'll get it back.
Ways your Baby Tricks You:
Problem: Your baby is not going to magically cease to desire to wear her costume after the holiday has come and gone. In my case, I sense, we will spend a lot of time playing bee and ladybug.
Solution: Make this a game and give it a name. This way, you can promise it, do it, and put it away when you're done. There is no reason your babies can't play dress up with their Halloween costumes for months to come. If you call it the Dress Up Game, or something similar, they won't be living in their costumes, and you've added another game to the pile to quell boredom on rainy days.