Disney look-a-like auditions are based on type-outs. They'll look at you and determine quickly if you have the right height and facial structure to be Anna or Elsa. I don't think there is a rule against wearing makeup, but typically audition tips are to keep it natural. They are looking to see if your facial characteristics match that of the other girls who are friends with princesses.
Ultimately, Disney has the right to choose only people who resemble the character. Also, I just want to let you know that is is EXTREMELY hard to be chosen as a face character; I have many gorgeous friends who look like princesses to me and were rejected. Also, the vast majority of people are fur characters first and then are eventually approved for face.
Good luck!