A couple of weeks ago, we tried to back out HF11 before applying FP1 on Domino 12.0.1.
Unfortunately, halfway through the back out process, we got the infamous "Related process is still running" error. The uninstall process crapped out and it then proceeded to deleted the recovery files (wtf!), so we were stuck in limbo and could not rerun the process.
As a result, we came up with the following steps to manually remove the Hot Fix. They worked for us, but your mileage may vary.
1. Shutdown the Domino server completely.
2. In the Domino program directory:
remove the Release1201 directory
3. Drop a copy of the following files from a 12.0.1 base build of Domino into the Domino Program directory
4. Open the Domino Server's Notes.ini and make the following changes:
Remove the three lines starting with the following from the Notes.ini file (they will likely be at the bottom of the file)
Restart the server.