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It's really overkill for just changing a single number -- but if he knows how to use a browser and MS Word, then he already has all the skills he needs so it would be a simple solution. I have several clients who use Contribute for keeping their calendar pages updated and we're having no problems after more than a year, even though they have only the most rudimentary tech skills.
If this is the only thing your client wants, then you may also be able to write a custom server-side script with a simple interface, tailored to this exact purpose.