It amazes me how many aspiring models will ask me what they need to do to their looks to attract a modeling scout or impress an agency. It amazes me even further when I get questions from girls that have been scouted and asked to come in for an interview, asking what they need to do to their hair, how they should take care of their skin, etc. It is common sense to know that if an scout showed an interest in you then your best bet is to show up to the agency looking exactly like you did when you were scouted. That means do not make an appointment to get a fancy hairstyle or buy a new wardrobe or slap a lot of makeup onto your face. You want to be recognizable to the scout and show the rest of the agency what potential the scout saw in you.
If you feel the need to change your hair in a drastic way, and are signed to an agency, be sure to run the idea past your agent first. It is important that they agree with the change because this means you will need to retake your portfolio pictures and headshots to reflect the new change. Never make such a drastic change to your appearance without running it by your agent but in the beginning stages when you have just been scouted, be sure to stay as you are. Let the agency fall in love with how you look naturally, don't feel the need to change yourself if it isn't even necessary.