Enacts changes on railway line (8)
I believe the answer is:
ancestry
'line' is the definition.
('ancestry' can be a synonym of 'line')
'enacts changes on railway' is the wordplay.
'changes' is an anagram indicator.
'on' says to put letters next to each other.
'railway' becomes 'ry' (abbreviation for railway).
'enacts' anagrammed gives 'ancest'.
'ancest'+'ry'='ANCESTRY'
(Other definitions for ancestry that I've seen before include "Lineage" , "race" , "Genealogy" , "Line of forebears" , "Blood line" .)