Train tours are subject to alteration (8)
I believe the answer is:
eurostar
'subject to alteration' is the definition.
I don't know anything about this answer so I cannot tell whether it can be defined by this definition.
'train tours are' is the wordplay.
'train' indicates an anagram (to train can mean to grow something into a shape).
'tours'+'are'='toursare'
'toursare' anagrammed gives 'EUROSTAR'.
Can you help me to learn more?
(Other definitions for eurostar that I've seen before include "The train from England to France" , "Waterloo to Paris train" , "International traveller" , "Passenger rail service from London to Paris, etc" , "Railway service via the Channel Tunnel" .)