Two main, and visibly obvious, changes were made to the locomotives when in traffic, viz: the fitting of Manson automatic tablet exchange apparatus for working single lines, and a rearwards projecting extension of the cab roof, offering more protection for the crew.
Five members of the class were renumbered between 1924 and 1927 when Nos. 3, 4, 5, 9 and 17 became Nos.