Need to find the replacement Code by using positions

[Sekars]

Hello Friends

Please refer the attached 2010 excel file all 4 sheets named A, B, C and D.

The Given Input code (In S18) will be removed with or without replacement code,
If replacement code is there then need to plot by formula in Cell (In Y18).

The light Green cells shows the input code which is being removed.

Need to find the replacement Code by using positions by using formulas.

Add and Remove will happen in same Position. In Some places Add will first and sometimes Remove will first.

Replacement code may be available or may not be.

I have used huge If Formula with helper formulas to find the result by checking the first 5 entries.

Is there any suggestions or new formulas avoiding If's or helper formulas.

Thanks in advance.