Swap joint with coppers (4,3,6)
I believe the answer is:
chop and change
'swap' is the definition.
I don't know anything about this answer so I cannot judge whether this works.
'joint with coppers' is the wordplay.
'joint' becomes 'chop' (joint of meat).
'with' becomes 'and'.
'coppers' becomes 'change' (coppers can mean small change).
'chop'+'and'+'change'='CHOP AND CHANGE'
Can you help me to learn more?
(Other definitions for chop and change that I've seen before include "Blow hot and cold" , "Vacillate - keep altering plans" , "Seesaw (metaphorically)" , "Move things around, often for no good reason" , "Repeatedly vary one's preference" .)