Hi Vikal,
Nilay has suggested in a better way.However, I would like to suggest that you can achieve the client's requirement by having only 1 Freight condition type which you have already configured. You may create a new Condition table using key combination of "Plant" and assign it in the existing Access Sequence which is already assigned to the respective Condition Type.Hence, your client would be able to create Plant-wise condition record using different rates.
Hope it helps.
Regards
Kamlesh