Alteration in the pub gets a warm welcome (10)
I believe the answer is:
innovation
'alteration' is the definition.
(thesaurus)
'pub gets a warm welcome' is the wordplay.
'pub' becomes 'inn' (an inn is a type of pub).
'gets' means one lot of letters go next to another.
'a warm welcome' becomes 'ovation' (I can't justify this - if you can you should give a lot more credence to this answer).
'inn'+'ovation'='INNOVATION'
'in the' is the link.
Can you help me to learn more?
(Other definitions for innovation that I've seen before include "original" , "What's new" , "New idea" , "Something new" , "Something introduced as a novelty" .)