Vamos ver o texto.
You make yourself look different until the spell ends or until you use your action to dismiss it. You can seem 1 foot shorter or taller and can appear thin, fat, or in between. You can't change your body type, so you must adopt a form that has the same basic arrangement of limbs. Otherwise, the extent of the illusion is up to you.
Parece bastante claro que você pode procurar como quiser. No entanto, as regras também afirmam:
If someone attempts to touch you, they will be able to pass through the illusion and learn that you are disguised. Otherwise, to discern that you are disguised, a creature can use its action to make an Intelligence (Investigation) check against your spell save DC.
Portanto, disfarçar-se é mais fácil "descobrir". Alter self realmente muda sua forma, mas também requer Concentração.