There are a few approaches you could consider here. Unfortunately, my crystal ball is on the fritz and my psychic skills are basically non-existant. So it's impossible for me to ascertain the particular version of RoboHelp you may be using. So I'll simply assume version 11 as that's the current shipping version.
Recent versions of RoboHelp make it really easy to create and maintain more than a single index. The following assumes you have created more than one index.
You could create multiple outputs, with each output using its own index. You simply duplicate one output in the Single Source Layout recipe box as many times as you need. Then you configure each output to use the desired index. After you generate, you end up with multiple sets of WebHelp files that would need to be published to different folders on your server. The end user would then need to have the correct link to open the set created for them.
The last two or three versions of RoboHelp offer a feature known as "Dynamic User Centric Content" or DUCC. This is also known as Content Categories. So with this approach you use a Single recipe in your Single Source Layouts pod. You define more than one category and you make the unique index assignment in the Category settings.
After you generate and publish, the end user is able to see the other categories, but they make the selection that applies to them.
Thank you, Rick. You are always quick to reply and identify new Robohelp functionality. Very much appreciated.