What is the meaning of "altering Allah's creation," and does this include the use of nail polish (manicure), removing body hair, or cosmetics that change a girl's appearance? Are these actions considered imitating the disbelievers?

There has been a detailed explanation of the criterion for dispraised alteration of Allah's creation. As for cosmetics, nail polish, and a woman removing hair from her body—excluding the eyebrows and head—the default ruling is that all of this is permissible and does not fall under the dispraised alteration of Allah's creation. The forbidden imitation of disbelievers applies only to practices exclusive to them. As for practices that have become widespread among Muslims and are not distinctive to disbelievers, they do not fall under that prohibition.