Sincerly, we are not sure to understand the issues that you are encountring with the L/C:
1- For the freight --> Since it is FOB, you can indicate on the BL : Freight to be paid at TUNIS
2- IMO number : condition 47A is a standard paragraph always introduced as it is by the bank. But, it does not harm if you do not indicate the IMO number on the BL. It is indeed acceptable.