Use keywords like SponsorG20120930 for sponsor deliverables instead of milestones

We're currently using Trac's milestone field for two things: version milestone and sponsor milestone. It would be good to assign a ticket to both a version like Tor 0.2.4.x-final and to a sponsor milestone like Sponsor G, September 30, 2012. Mike and Nick suggested to use Trac keywords for this purpose.

Two questions:

Is SponsorG20120930 a good format for such keywords?
Is there an easy way to modify existing tickets in bulk? I don't mind so much doing it manually, but it's going to generate a lot of emails.

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