If anyone knows how to make it happen, it will be Willam. Perhaps he will pop in and advise.
No sorry this is not possible, but you may want to look at using the Dynamic User Centric Control functionality to have a drop down that specific sets of users could use to limit the content they see. It is available from RH9 or later. See Dynamic User-Centric Content (DUCC) generation in RoboHelp 9 « Technical Communication Suite for more detail.
Whether you can do this depends on how much time you are willing to invest. The easy answer is 'no'.
Having said that, it is possible to change the script to change the icon for a specific page. For this, you need to change the output files and you must create an exception to the regular mechanism. Best of all, you need to hard code the topic title/url to do this. This is a typical case of 'I offer consultancy for these kinds of things'. PM me if you want to know more.
So, who gets the "Correct Answer" award ??? I'll have to go with Cap'r. He was first to reply. Thanks to Captiv8r, Robocolum(n), and WvW. I would love to have a unique icon for one book but there's no budget, etc. and no time for me to learn JS.