Yes as colucix said you can use vi to edit, at the command line type vi /path/to/file.name I don't mean literally just vi and a space then the path to what ever file you want to edit. After vi opens the file use the arrow keys to move the curser to the spot you need to edit. Press i for insert, to insert text, when you are done press the Esc key to take you out of insert mode. To save the changes you made press Shift colon at the same time, this will alow you to enter a command in the lower left side of the screen. Now type wq w=write q=quit and press enter, that should do it.
My advice is to learn how to get around using vi for just such a time as now.
NOTE: WARNING I think you will need to be logged in as root to make the changes to that file.