You could add a reducer ring for standard freewheels but it'd be 2.4 mm thick, so difficult to put a tool on (which you'd need to to make sure you can separate the freewheel from the reducer and the reducer from the hub).
@Emyr started
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You could add a reducer ring for standard freewheels but it'd be 2.4 mm thick, so difficult to put a tool on (which you'd need to to make sure you can separate the freewheel from the reducer and the reducer from the hub).