Any changes that are made to the Project's Scope outlined in the signed version of the Project FSD will be added as an addendum to the document, be considered a change request, and will be dealt with on an as-needed basis.
The best practice is to keep all of your change requests in the designated folder (Financial > Change Requests).
Although the FSD should be kept up throughout the course of the project, if all change requests are executed and kept in their proper location, one can always go back and add them as addendums to the FSD.