It looks to me as if what you really are trying to do is to add a column to the imported csv file.
Using the LOADCSV2 you actually end up with two objects to manipulate, the headers which is a list, and the data which is a list of arrays. So you need to insert data into both objects in the correct places in the row.
And you need to add data to the relevant place for each data row.
Have a look at the attached project which achieves this on a simple level.
It depends on what you are trying to do as to whether this is actually worth doing, it may be easier to change the source csv, and if there are going to be lots of changes. it may be better to convert the imported data in to a different data structure or database.