Is there a way to set the current module image to something other than HEAD even if someone wants the current default image? (So that a rack isn’t following the HEAD image, and doesn’t update when a new image is uploaded.)
-- chaos215bar2

simply choose everything but not HEAD

image

image

EDIT
ensure you have enabled the panel selector (top right of the rack)
image

further i misunderstood your question :D
in my opinion it makes sense to have modules default image set to HEAD because there are often improvements in quality or perspective.