Change railway after Virginia (4)
I believe the answer is:
vary
'change' is the definition.
('vary' can be a synonym of 'change')
'railway after virginia' is the wordplay.
'railway' becomes 'ry' (abbreviation for railway).
'after' says to put letters next to each other.
'virginia' becomes 'va' (US state abbreviation).
'ry' 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" .)