"Edit the target". Do you mean edit the shortcut on your desktop/start
menu? Just right-click and choose properties. You will see the "Target"
field, and you can add your parameters after whetever is already there.
Remember to leave a space between each parameter you add.

Before we go any further, is this for HL1 or 2? If it's for HL2,
there's a setting in the options somewhere which activates the console.
Then , in game, you press the key to the left of the "1" on your
keyboard (called the tilda key, because on US keyboards the tilda
character (~) is on it).