Am I allowed/recommended/supposed to edit this file?
If a copy of eio.cfg is edited offline, can/should it be FTP'ed to the bot to replace copy in /SYSPAR?
Yes, you can and should edit this file to Configure your I/O´s.
If you have a Profibuscard or other E/O Boards, you have to declare them in eio.cfg.
Are comments possible within the file and if so, how?
Well, if you put a # in the beginning of the Line.
Is the file only read at boot time?
Yes, you always need an Reboot.
I find nothing in my documentation about direct edit of eio.cfg, is there any documentation available?
I am looking, but also find nothing in that Moment.
When I change IO setup from pendant I do not see time/date of this file change. Is there another copy somewhere else on the filesystem?
No, i know only that one in /SYSPAR
i have attached a eio.cfg from us with Profibus Card and Standard I/O's.
Hope it is a bit useful.