Dear Mojca:
...it permanently so that I can invoke it in all my documents? I was unable to find instructions in the ConTexT garden for this, and what I could find on the archives was not helpful (something about "running mktexlsr" and/or "texhash" that I have don't know how to do in OS X, and would be afraid to do without instructions anyway for fear of screwing up my TeX distribution).
You can put the file to any location where TeX can find it. For example if the file context.tex is located under [somepath]/texmf[-local]/tex/context/base/context.tex you might put the file to [somepath]/texmf[-local]/tex/context/third/t-amsl.tex (but basically any location under "texmf" would do).
... and then run mktexlsr without any additinal arguments.
You cannot screw up your TeX distribution by running mktexlsr or texhash: they're only meant to refresh the database (to know which file is where). Either of the commands should be present on your distribution I believe (most probably mktxlsr).
Mojca
Thanks. The previous response on the list solved this particular problem, but for future reference, how do I "run" mktexlsr? from the OS X Terminal? I have never used that before, so I would need pretty basic instructions (e.g. would I have tell the Terminal where to find "mktexlsr"?). I appreciate your help! Tom