To highlight two key points from Peter that I was going to respond with:
1) In a goal race, don't do anything new. That includes wearing a new pair of shoes.
2) When it comes to shoes, while there may be general guidelines (such as racing in shoes lighter than your trainers will help you go faster) we are all studies of one. I personally go for as light as possible for races of basically any distance but a lot of people can't wear shoes I wouldn't hesitate to pull out, for example, for a half marathon because the shoes would be too minimal for them.