On the Review ribbon in the Comments section, I see there is an Add icon. Otherwise though I think the only way you could add your other requirements is by adding to the generated PDF and I suspect that would screw up the import process.
As an alternative, what I did before Review was added to RoboHelp was create a Word document. In the topic when editing I would prefix any change with three hash symbols to facilitate searching and quick visual recognition. There I was free to add whatever comments I wanted and the reviewers were able to work in Word, which they were familiar with. The downside, of course, is there is no import functionality. Before releasing any help, I would check for ### in the output to ensure nothing had been missed.
See www.grainge.org for RoboHelp and Authoring information
Currently, my workflow is to create a word document with all the topics that will be changing or new topics. I mark changes with a comment bubble. Send to review and the reviewers would make changes in the document itself. (I have track changes on). Once the document is finalized, I would then make the changes in Robohelp. The problem with this method is that copy and paste sometimes brings in unwanted characters, the bullets don't translate correctly, and I end up having to rework the edits in robohelp to get the formatting correct. Sometimes I have to paste line by line to ensure that the formatting is correct. Even when I use my styles in robohelp.
To save time and the rework, I am proposing to do the changes in Robohelp directly. Then use the PDF for review functionality in Robohelp for review. Once the reviewers have completed their changes, I can import it in and then I'm done. Should be half the time, will cut down on mistakes made from transferring word changes to Robohelp. So the test cycle would be only testing links and not have to deal with content bugs.
Only problem is that the Help Document has had a format that people are used to and I would like to keep that format. If there is any other way to do this type of workflow, I'm up for any ideas?