With the release of Soundpaint 3.0, Soundpaint now allows you to make custom labels for different ranges of the keyboard on both premade and user programs.
To add a range label, open the keyboard view by clicking the keyboard button in the bottom right of soundpaint.
From there, hover your mouse over the key you want to set your label on, and click the "+" icon that appears. This will spawn a range label.
Once this is done, you can change the label name, colour, and range to fit your preference.
More information can be found in our Soundpaint 3.0 Walkthrough: