source: This Agreement may only be amended by a writing specifically referencing this Agreement which has been signed by authorized representatives of the parties.
target: This Agreement may only be amended by a writing.  The writing must be specifically referencing this Agreement.  The Agreement has been signed by authorized representatives of the parties.
references: This Agreement may only be amended by a writing.  The writing must be specifically referencing this Agreement.  The Agreement has been signed by authorized representatives of the parties.