In build mode, right-click on the text box and select "Enable Scripting".
Then the code to set it is (this is from memory):
Text1.Contents = "Hey, this works!"
Right, as David pointed out, "static" elements need to be "enabled for scripting". Dynamic elements (e.g. Trend) automatically are.
And I can confirm that the line of code David provided from memory is fine :)
indeed it does!....