Contrary to what many believe, publication agreements are negotiable. While it may be intimidating to think about negotiating with a publisher, doing so can help you secure rights that will allow you to retain more control over your work. The more control you have over your research, the better positioned you are to be proactive in making your work discoverable and accessible to potential readers.
It may be helpful at the outset to think about the agreement the publisher gives you as a request rather than a command or ultimatum. Remember, until you say otherwise, you are the owner or your work, and you have to give the publisher permission to use it. Publishers rely on researchers like you to produce material for them to publish, and many will be willing to work with you to reach an agreement that is satisfactory to both parties.
Prior to asking for any modifications to the initial agreement, think about what your goals are. What do you want that is not offered in the initial proposal? You may also need to adjust your goals based on the terms of the original proposal. If the publisher is asking for a complete transfer of copyright, then they will probably be unwilling to modify the agreement to allow you to retain your copyright. However, they may be willing to allow you to retain certain specified rights.
Author's Addenda are legal tools that authors can use to modify the terms of publishers' agreements to allow for the retention of additional rights. In order to take effect, these addenda must be signed by both teh author and the publisher, and publishers may not be willing to accept an addendum, at least not without making some modifications. For this reason, it's best to think of authors' addenda as tools for negotiation. They can provide you with some ideas of what to ask for, and provide sample language that you can modify to suit your purposes.
The SPARC Author Addendum is the most well-known addendum. However, Creative Commons also has a Scholar's Copyright Addendum Engine that will generate a PDF that can be attached to a publisher's contract to request the rights you wish to retain. Examples of other addenda include the Big Ten Academic Alliance Authors Addendum, the University of Michigan Authors Addenda.