If you copy the dataset into a simple list you can do it with the following:
products = [
[ 1, 200, 'X' ],
[ 2, 300, 'A' ],
[ 2, 400, 'A' ],
[ 2, 200, 'A' ],
[ 3, 500, 'A' ],
[ 3, 400, 'A' ],
[ 3, 300, 'B' ],
]
for i in range(len(products)):
if products[i][0] == 3:
products[i][2] = 'B'
print(products)