We don't currently offer the ability to set the desired performance, although it is something we are interested in exploring further in future.
The main challenge with doing this is that these are perception-based assessments, so setting a '4' desired score might mean something specific to you, but perception will vary across others in the organization. As a result, some people might regard 4 out of 5 as a basic starting point (but feel employees should aim for a 5) and some might believe employees will never reach a 5, so an aim of 4 is appropriate.
We've seen this result in 1-hour feedback-review meetings that argue about where the employee should aim to be & how this varies across the behaviors, so fail to get time to make a plan of action.
Instead, we recommend using a dual rating scale where everyone can provide context to their answers, or a single rating scale where everyone should aim for top marks in everything. We explain why in our Why we compare current and desired performance help article.