Give power to chosen railway, if included (9)
I believe the answer is:
electrify
'give power to' is the definition.
(provide with electrical power)
'chosen railway if included' is the wordplay.
'chosen' becomes 'elect' ('elect' as an adjective can mean chosen).
'railway' becomes 'ry' (abbreviation for railway).
'included' is an insertion indicator.
'ry' enclosing 'if' is 'rify'.
'elect'+'rify'='ELECTRIFY'
(Other definitions for electrify that I've seen before include "Supply power to; shock, thrill" , "Charge - excite greatly" , "Charge with power" , "Galvanise - animate" , "Cause thrilling excitement in (someone)" .)