On Wed, Jan 12, 2022 at 1:27 PM G. Branden Robinson <g.branden.robinson@gmail.com> wrote:

An argument could be made for the word "replacement", but I've found it
useful to reserve that plain-spoken term for discussion of things a
human might do (perhaps in the course of editing a document or
developing a macro).  To my ear, "interpolation" sounds fancy enough to
refer to something you let a machine do, without being _excessively_
technical in tone.

Strictly speaking, what is interpolated is the _contents_ of the register, not the register itself.  It never hurts to be too clear.