Laura, it does say "unless in writing and signed by both parties" so you may be fine with a separate contract as long as it is signed by both parties, but it would probably be better if you can work out the entire arrangement within a single contract.

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Emily S. Damstra
natural science illustration
Waterloo, Ontario
(519) 616-3654
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www.emilydamstra.com
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On Thu, Jul 18, 2013 at 1:40 PM, Laura K. Jordan <[log in to unmask]> wrote:
Thank you all for your quick and very helpful comments, the contract has this entire agreement clause:

ENTIRE AGREEMENT.  This Agreement constitutes the entire agreement and understanding between the parties and shall not be modified, altered, changed or amended in any respect, unless in writing and signed by both parties.

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