Five on a railway making change (4)
I believe the answer is:
vary
'change' is the definition.
(I know that change can be written as vary)
'five on a railway' is the wordplay.
'five' becomes 'V' (Roman numeral).
'on' is a charade indicator (letters next to each other).
'railway' becomes 'ry' (abbreviation for railway).
'v'+'a'+'ry'='VARY'
'making' is the link.
(Other definitions for vary that I've seen before include "Make changes to" , "Change according to circumstances" , "Change, diverge, deviate" , "Fluctuate" , "Differ; change" .)