Rename CSV header using command line tools

This should do it:

https://stackoverflow.com/questions/11145270/bash-replace-an-entire-line-in-a-text-file

The header should just be the first line in your file, so if you use N = 1, and rewrite the line with the desired headers, so:

sed -i '1s/.*/One, h2, Three/' file.csv

will do it