pumpkinpoppet
^Advice needed - DS refuses to dress as an inn keeper with the other 180 (I kid you not) pupils. He insists on being a spaceman. He has no clue about the point or the story, just that he is singing some nice songs. And as far as he's concerned, if he has to dress up, then a spaceman it is.
We were sent a letter asking us to dress our children as inn keepers, but that the alternative could be an angel. So I suggested a spaceman outfit with fairy wings. But no - DS has 'compromised' by adding a cape and crown to the silver jumpsuit - to be a king. When asked the teacher seemed a bit indifferent to the costume choice.
Am I going to get snowballed by the other parents^
You could try boxing clever, tell him his spaceman is on a secret space mission, & needs to go in disguise....as an in keeper....or better still come up with something else, with the same costume 
other than that, IME the decent parents won't worry at all, & will probably see it as sweet - & any that don't aren't worth the effort of worry 
Thinking back, I remember our friends Son dressing as Spiderman for a Xmas play...he wouldn't wear anything else for months, so it was normal clothes for him, I remember lots of giggles over it, but nothing nasty at all, most thought he was adorable - so don't worry