You can add text to an influence by right-clicking on the influence and selecting Add Label from the context menu, or Shft+double-clicking on the influence (double-clicking on the influence while pressing the Shft key). This will add a textbox to the influence with the word "Text" inside (which you can subsequently replace with your own text).
You can edit the properties of the label (e.g., font, color, outline) by right-clicking on the influence and selecting Properties…. This dialog is similar to that used to edit the properties of text objects in the graphics pane.
To delete the text associated with an influence, select the text box, and press the Delete key.
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