In Colorado does a codicil need to be notarized and witnessed or just notarized.

There are no minor changes to a will if done improperly. While Colorado law now allows for mere notarizations of wills, most attorneys still prefer two witnesses and a notary, to ensure no questions if probated in another state. A codicil to make a simple revision would typically cost a couple hundred dollars if done by an attorney, small price to get the job done right (and they may review the will and point out other changes that should be made as well).

It must follow the same procedures as a will.

Attorney Durr has answered your question but your best bet would be to have an attorney do this for you. Often a new will will be written instead of a codicil for about the same price.

Codicils absolutely should follow the same formalities as the original will. However, as noted by one of the other attorneys, with today's word processing often it is just as easy to redo the entire will. If you decide to do it yourself it is highly recommended that you at least have a lawyer review it. Wills can be tricky, and It is very easy for laypersons to make inadvertent mistakes and ambiguities.