Change railway after Virginia (4)
I believe the answer is:
vary
'change' is the definition.
(synonyms)
'railway after virginia' is the wordplay.
'railway' becomes 'ry' (abbreviation).
'after' is a charade indicator (letters next to each other).
'virginia' becomes 'va' (US state abbreviation).
'ry' put after 'va' is 'VARY'.
(Other definitions for vary that I've seen before include "Make a change in" , "Change form or state" , "Make or become different" , "Fluctuate" , "Differ; change" .)