Mixes every halved shellfish… (6)
I believe the answer is:
alloys
'mixes' is the definition.
The answer and definition can be both related to change as well as being verbs in their -s form.
Perhaps they are linked in a way I don't understand?
'every halved shellfish' is the wordplay.
'every' becomes 'all' (similar in meaning).
'halved' indicates taking half.
'shellfish' becomes 'oyster' (oyster is a kind of shellfish).
'oyster' with half the letters taken is 'oys'.
'all'+'oys'='ALLOYS'
Can you help me to learn more?
(Other definitions for alloys that I've seen before include "Blends of metals" , "Metals formed from mixtures of other metals" , "Puts down" , "Tempers" .)