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So I do as you say and edit my auto-fill information.

How can I specify which one of my several email addresses to use?

I see no way of doing that.
 
Solution

I resolved this by making one card with just the info that I wanted to use in Autofill, and one card with all the other info (I added the word EXTRA in the suffix area of that card, so that it would be easily distinguishable from the one I use for autofill).
 
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