Suppliers should be paid fairly, and I'm glad the fines actually seem meaningful (in theory, anyway; those are maximum penalties. I doubt they'll actually get applied any time soon). It won't help the average consumer tho.
Supermarkets here use their position as middlemen to squeeze both ends of the supply chain; they short their suppliers and price gouge their customers. The code of conduct only fixes one side of this. It applies purely to dealings with suppliers, and has nothing to do with retail pricing.
It's more likely retail prices will increase to maintain the profit margin. Line must go up and the plebs just have to suck it.