Record by socialist got thinner (7)
I believe the answer is:
tapered
'got thinner' is the definition.
The answer and definition can be both related to change as well as being past participle verbs.
Maybe you can see a link between them that I can't see?
'record by socialist' is the wordplay.
'record' becomes 'tape' (taping is a kind of recording).
'by' is a charade indicator (letters next to each other).
'socialist' becomes 'red' (red can informally mean a socialist).
'tape'+'red'='TAPERED'
Can you help me to learn more?
(Other definitions for tapered that I've seen before include "Gradually narrowing" , "Coming to a point" , "Narrowing towards one end" , "Becoming narrower towards one end" , "Became gradually narrower as candle may" .)