s/\G(?|(\0{16})+(?{'*'})|(.{1,16})(?{...}))/$^R\n/sgr  What you used.
s/\G(\0{16})|\G.{1,16}/($1?"*":...)."\n"/segr          Could be used.
s/\G.{1,16}/($&eq"\0"x16?"*":...)."\n"/segr            What I used.