"Я майже інша людина."
Переклад:I am almost another person.
Human tends to be used when you're being more scientific or talking about our species in general. Person is used when you're talking about an individual, and we use person/people more in everyday conversation. For example we would say "have you seen those people by the river?", it would sound odd to say "have you seen those humans by the river?".
"I am almost another person" suggests your character has changed a lot. "I am almost another human" suggests half of your body parts have been changed for someone else's.