I argue that the Conceptual Ethics and Conceptual Engineering framework, in its pragmatist version as recently defended by Thomasson (2017, 2020), provides a means of articulating and defending the conventionalist interpretation of projects of conceptual extension (e.g. the extended mind, the extended phenotype) in biology and psychology. This promises to be illuminating in both directions: it helps to make sense of, and provides an explicit methodology for, pragmatic conceptual extension in science, while offering further evidence for the value and fruitfulness of the conceptual ethics/engineering framework itself, in particular with respect to conceptual change within science, which has thus-far received little attention in the literature on conceptual ethics/engineering.