A contigency plan should include:
Contingency mechanism: (What to do? Who will do it?)
Contingency deadline: When is the last time the contingency mechanism can be put in place?
The contingency deadline will most likely be the beta freeze. In some cases, it may be more appropriate to set it to the start of the mass rebuild or branch day. Rarely, you can use final freeze, but this should only be used for Changes that are trivially-revertable.
Is there upstream documentation on this change, or notes you have written yourself?
Link to that material here so other interested developers can get involved.
Release Notes
The Fedora Linux Release Notes inform end-users about what is new in the release. Examples of past release notes are here: http://docs.fedoraproject.org/release-notes/ The release notes also help users know how to deal with platform changes such as ABIs/APIs, configuration or data file formats, or upgrade concerns. If there are any such changes involved in this change, indicate them here. A link to upstream documentation will often satisfy this need. This information forms the basis of the release notes edited by the documentation team and shipped with the release.