Boot your Tecra M5 from the maintenance floppy. Select option 2: Repair initial config set. This is supposed to shut down your system when it finishes, but it failed to terminate on my laptop. Eventually I removed the floppy and rebooted my Tecra M5 laptop.

The Settings/System/About dialog now shows the updated CPU.

The device manager now shows the updated CPU.

Running the maintenance tool is also supposed to cure the problem of the fan running at full speed following a CPU upgrade.