# insert header
cat some_file | sed '1i #new first line'

# edit file
sed -i '1i #new first line' some_file

echo -e "start transaction;\n$(cat xaa.sql)" > xaa.sql

$ cat insert-sql.sh
sed -e'1i\
insert into my_table (col1, col2) values ' -e'1s/^,/ /' $1