If so, look for some feature that causes Aperture to re-read metadata on changed files.
I'm fairly certain this command does not exist in Aperture, but I don't think it is necessary (see below).
I
can do what the OP has described for
JPGs, but I've never tried this in Raw files (I choose use sidecars for my Raw files rather than embedding directly into the file).
To the O.P. - can you try the same experiment with JPGs? The result would tell us if this is issue specifically with embedded metadata Canon/Raw files, or a general Aperture issue.. (i.e. the experiment should work for embedded metadata in JPGs).
However, for handling JPGs like this, one really nice feature of Aperture that I did not count on is this:
Once I've imported (as a 'referenced' file) an image to Aperture that has been keyworded with PM, not only does Aperture "see" the keywords, but it will update *live* if I make other keyword/metadata changes to the referenced file using PM. This avoids the need to tell the application to "re-read" the file to pick up metadata changes made externally by PM. I've never seen this Aperture behavior described or documented anywhere but it makes my life easier in using Aperture at the back-end of my workflow just for cataloging, and PM/NX2 for everything else. Thought I'd share in case it's useful for any Aperture users out there. It's made Aperture + PM work together better than I had anticipated.
Chris