Haircut on kid is one way to ring the changes (3,5)
I believe the answer is:
Here is my best explanation:
'one way to ring the changes' is the definition.
'haircut on kid' is the subsidiary indication.
'haircut' becomes 'bob'.
'on' means one lot of letters go next to another.
'kid' becomes 'minor' ('minor' can be a synonym of 'kid'**).
'is' is the link.