For Cyclic 10i, using tfloader at the command prompt didn't work. I did, however, find a workaround, sort of a minor nuclear option. Perhaps it's not global thermonuclear, just a bit of a regional reset, but what I did was to reload the initial tax master base file over the top of my existing data set, using the master file associated with cyclic 10i. That took about 15 minutes (and had a web page timeout at the end, but it was still successful), and when it was done my system was at Cyclic I and Bulletin 63.
I confirmed with the "out" file (found at \Apache...\Tomcat...\PRD\temp\###_TFU10063.PKG(tf.xml).out) that all the various records were processed successfully, no errors.
The SAP current tax mappings and license key, audit log messages, etc, were all left intact. Really, in some ways, this was easier than manually loading the new cyclic and all the bulletins individually anyway.