Hi @m.greffet,
do you start the form from Grasshopper or from Rhino ? In the latter case, you can access Grasshopper with the PluginObject to feed a definition with data. A simple example is shown here and the available methods here. (I guess the number of methods changed since 2013).
To have a much deeper access from a script started within Rhino and Grasshopper, you might try NodeInCode.
_
c.