Change header of all text files in directory in commandline
This will remove first four lines form csv files and remove "(Absorbance)" part from them:

find . -name  "*\.csv" -exec \
    bash -c "tail -n +5 {} |
                 sed 's/Absorbance(Absorbance)/Absorbance/' |
                 sed 's/Elapsed Time/ElapsedTime/' &gt; {}.bak |
                 mv {}.bak {}" \;