I'm assuming you're following the rules regarding cookies.

If all you want to do is add to an existing cookie, it's probably easiest to:

1. Read the existing cookie data into a variable.
2. Add (concatenate) the new data to the variable.
3. Rewrite the cookie, now with the added data in the variable.

If the new, updated cookie has the same name as an existing cookie, it'll just overwrite it.

Good luck, db