Originally Posted by knc1

Probably the easiest way would be to boot to the alternate OS ('diags') and then use that system to re-install either 5.8.10 or 5.8.11
I don't think you have time to write the old jar file in the few seconds the normal OS gives you.
So the only way (if you don't have Rescue Pack with the Cowards Rescue Pack extension) is to use the serial port.

The "DO_FACTORY_RESTORE" does not modify the system image files, so it will not "fix" the damaged system image.

The "hotfix" code (that is, the "bridge code" part of it) has a way to boot an "emergency script" during normal start up.
I am not sure if that will help in this situation.
I do not recall anyone providing example scripts.