How can I fix my Hotpoint refrigerator, model R134A?

This refrigerator has two thermostats working in parallel. The one in the main food cabinet does not maintain freezing conditions but is working correctly. The second thermostat supplied via a N/C contact on the first is not working and is located in an inaccessible part of the fridge body. I would like to try a cheap option by replacing the working thermostat with one set at a lower temperature range (below freezing). The existing part number I wish to replace is HOT282040.