Certainly you can implement a “LinkDrawn” DiagramEvent listener that modifies the newly drawn Link (the e.subject) or its e.subject.data. See How to insertLink custom data for link while drawing link - #2 by walter
If you are asking about changing the data earlier, that is also possible – it depends on when.
For example, before a link is drawn by setting LinkingTool.archetypeLinkData: Add an extra property in the linkData during link creation
Or perhaps at LinkingTool.insertLink time: I want to catch drawing link event before the drawing has finished - #7 by walter