def test_append (list1):
    res = []
    for elem in list1:
        res.append(elem )
    return res

def mod_list (list1):
    modified_list = test_append(list1)
    for elem in modified_list:
        elem[0] = 'A'
        elem[1] = 'B'
    return modified_list

my_list = [[1,2], [3,4], [5,6]]

print(my_list)
result = mod_list(my_list)
print(my_list)
print(result)