Seldom real changes in the railway (6)
I believe the answer is:
rarely
'seldom' is the definition.
(I know that rarely can be written as rarely)
'real changes in the railway' is the wordplay.
'changes' indicates an anagram.
'in the' indicates putting letters inside.
'railway' becomes 'ry' (abbreviation for railway).
'real' with letters rearranged gives 'arel'.
'arel' placed into 'ry' is 'RARELY'.
(Other definitions for rarely that I've seen before include "when hundred-to-one horse wins?" , "very well" , "once in a blue moon" , "Seldom, not frequently" , "Gas used in fluorescent signs" .)