Had called at half past and mended the racket (6)
I believe the answer is:
strung
'had called at' is the definition.
The definition and answer can be both related to change as well as being past participle verbs.
Maybe they are linked in a way I don't understand?
'half past and mended the racket' is the wordplay.
'half' suggests halving the letters.
'and' says to put letters next to each other.
'mended the racket' becomes 'rung' (I am not sure about this - if you are sure you should believe this answer much more).
'past' halved is 'st'.
'st'+'rung'='STRUNG'
Can you help me to learn more?
(Other definitions for strung that I've seen before include "(Of piano) given wires" , "Like a violin or racket?" , "Threaded" , "suspended" , "Like violins and tennis racquets" .)