The stick changes its model when 'custom_model_data' is set to '12345'
The item frame 1 (left) contains a 'stick' with 'custom_model_data=12345'. The item frame 2 (center) contains a 'golden_sword' with 'custom_model_data=12345'. The item frame 3 (right) contains a 'potion' with 'potion_contents={"potion":"water"}'.
The model is registered for the "stick" item on the "custom_name" component. To replace the model, simply rename the item on the anvil