The term for moving a body part to take over a function without removal is "transfer." In medical terminology, transfer specifically refers to relocating a body part, such as a graft or segment of tissue, to a different site in the body for functional purposes. This often can be seen in procedures like tissue transfer in plastic surgery, where a body part is moved to provide coverage or support to another area while still maintaining its blood supply and functionality.
Repositioning typically involves adjusting the position of a body part but does not inherently imply taking over a function. Mobilization refers to the process of moving or enabling movement in a joint or body part, often in the context of physical therapy or rehabilitation, rather than transferring a function. Reimplantation usually involves reattaching a body part or tissue that has been removed, thereby indicating a return rather than a transfer for functional takeover.
Given these definitions, "transfer" accurately describes the act of moving a body part for a functional purpose without removing it.