变性 is a noun with two main clusters of meaning. In medical/social contexts it refers to sex change or gender transition (often in compounds like 变性手术 'sex reassignment surgery' or 变性人 'transgender person'). In scientific contexts it means 'denaturation' (e.g. protein denaturation). Although the word can colloquially be used as a verb (他去变性了), the formal POS is noun — you will most often see it as the head of a compound or as a topic noun. Pay attention to context to distinguish the transgender sense from the chemistry sense.