So easy to perform!
I first, downloaded the 32-bit and 64-bit Anyboot variants of HRev51911, unpacked the ISOs and burned them. I then tested them for being bootable with a Thinkpad T60 (T7200 CPU - X64 capable CPU) as it was the only system with an internal optical drive I had access to. This T60 also does not have a hard drive - so no fear about messing up the internal hard drive!
I decided to recycle the USB Flash Drive on which I had previously installed HRev51877 using Etcher.
To minimize risks, I clean-formatted the USB Flash Drive using the HP USB USB Format utility for Windows (.HPUSBFW.exe - Version 18.104.22.168). This put back the flash drive in the same state and took a bit more than one hour for the 16 GB drive.
Booted the T60 with a SystemRescueCD and the USB Flash Drive inserted into a port. Using GParted, the space on the flash drive was divided into three - 1/4 for Haiku-32bit, 1/4 for Haiku-64bit, and 1/2 as a BFS share volume.
Booted the 32-bit disc. Using DriveSetup, the first partition was formatted to BFS and named. Then the Installer was run.
Booted the 64-bit disc. Using its DriveSetup, the second partition was formatted to BFS and named. Then the installer was run.
The third partition was then formatted to BFS and named.
Finally, BoorMan (in ~/config/settings/bootman/) was run and a copy of the MBR saved to the BFS shared partition. Also, a default time-out for booting into the 32-bit variant was set.
I tested both variants on the Thinkpad T60. I re-tested on the Aspire One 721 (AMD Ahtlon II Neo K125 CPU). No major issues in all cases and no need to boot via Safe Mode.
With the installation order I followed, the name of the 32-bit variant is blue and the of the 64-bit variant is red. The colors really looked like the old blue and red of the BeOS logo - nice memory!