He can't "incarnate again" because His sacred humanity and divinity cannot be separated since when He assumed flesh in the womb of the Blessed Virgin Mother Mary.
Council of Toledo (685 A.D.), Denzinger 283:
In this Son of God we believe there are two natures, one of divinity, the other of humanity, which the one person of Christ so united in Himself that the divinity can never be separated from the humanity, nor the humanity from the divinity.
In quo Dei Filio duas credimus esse naturas; unam divinitatis, alteram humanitatis, quas ita in se una Christi persona univit, ut nec divinitas ab humanitate, nec humanitas a divinitate possit aliquando seiungi.
cf. pt. 2, ch. 1, §3, "Thesis II: The Logos never even for an instant dissociated Himself from His manhood." of Christology: A Dogmatic Treatise on the Incarnation by Pohle
Christ is present after consecration not as though He departed from heaven and returned to earth but "after the manner of substance" (secundum modum substantiæ).