Traditional publishing models may require you as an author to assign some or all of your ownership rights to the publisher of your work. Doing so, however, may constrain your ability to use and determine access to your work. Suggested ways to publish your works without giving up all of your copyright interests are offered by the following organizations:
Note that most publishing agreements contain a clause whereby the parties agree that there are no other agreements or representations between the parties. Thus if you wish to use an addendum that is binding and enforceable, the main agreement should either include a provision that expressly incorporates the addendum, or the addendum should be signed at the same time as the publishing agreement as a stipulated component of the agreement1.
1 The information provided on this site is offered as general guidance only, not as legal counsel.