I edited my local.cf file, but SpamAssassin isn't recognising the changes.

spamd compiles and stores the system-wide rules on start-up to speed up processing. If you edit the local.cf file, you should restart spamd so it can re-read the settings.

A nice enhancement in 3.0 is that if you run spamassassin or spamd with the -D (debug) flag, the specific configuration files (and the order used) are shown