From what I see it seems these are out of the box and not configurable on a professional-only platform. When I did some research on them, it looks like they are pretty much static. I can look further into it, but from I don’t’ see that those text is configurable. Only thing you can add/edit/delete in the professional is risk categories.
Impact tab - Risks Details (P6 Professional Only)
Use the Impact tab to enter pre-response, response and post-response information, and to view calculated pre- and post-response scores.
Select values in the Pre-Response section to characterize the potential risk in terms of its likelihood of occurring (Probability field), its impact on the schedule (Schedule field), and its impact on cost (Cost field). Together the Schedule and Cost fields are called the impact fields. The application uses the values from the probability and impact fields to calculate a Score, also shown on this tab.
If you choose to respond to a risk you can use the fields in the Response and Post-Response sections. Using the Response fields enables the Post-Response fields. The fields in the Post-Response section mirror those in the Pre-Response section, but they are used to measure the significance of the risk based on the response.
Probability: The probability of the risk occurring.
<None> (Clears a previous selection, if any.)
1 - Very High (70% or higher)
2 - High (50% to 70%)
3 - Medium (30% to 50%)
4 - Low (10% to 30%)
5 - Very Low (Up to 10%)
6 - N (Negligible)