The word may remain unchanged; what differs is the scope of the signified meaning.
“Human” → rational animal: the complete meaning, hence muṭābaqah.
“Human” → animal: one conceptual part, hence taḍammun.
“Human” → rational: another conceptual part, also taḍammun.
A hand is physically part of a human body, but it is not therefore a component of the classical definition “rational animal.” To assess taḍammun, first identify the assigned concept.