Tried it, but it doesn't work. I can add the line to the Pref file, and save it just fine with File Sharing off. After I try and fail to connect with the OS 9 Mac, the line is no longer in the pref file.
It looks like your hack was more of a 10.4 solution. 10.6 is very different.
It appears that the client will have to have AFP 3.0 or higher, which means Mac OS X. OS 9 introduced AFP 2.2, and it's not cutting it anymore.