I think for <1MB of data, with changes once (or twice) a year, the correct API is a static webserver with working ETag/If-Modified-Since support.

If you want to get really fancy, offer an additional webhook which triggers when the file changes - so clients know when to redownload it and don't have to poll once a day.

...or make a script that sends a predefined e-mail to a mailing list when there is a change.