Reorganisation of trains by Conservative is short-lived (10)
I believe the answer is:
transitory
'short-lived' is the definition.
(synonyms)
'reorganisation of trains by conservative' is the wordplay.
'reorganisation of' indicates an anagram (I've seen this in other clues).
'by' says to put letters next to each other.
'conservative' becomes 'tory' (informal term for a Conservative Party member).
'trains' anagrammed gives 'transi'.
'transi'+'tory'='TRANSITORY'
'is' acts as a link.
(Other definitions for transitory that I've seen before include "Ephemeral" , "lasting long" , "Brief" , "Fleeting" , "Here-today-gone-tomorrow" .)