By the way, I realized where my original flawed code came from: The FrameMaker 10 Scripting Guide, p.6. It gives this sample:
var doc = app.ActiveDoc;
var tl = new TextLoc();
var firstPgf = doc.MainFlowInDoc.FirstTextFrameInFlow.FirstPgf;
tl.obj = firstPgf;
doc.AddText (tl, "Hello");
doc.AutoChangeBars =1;
FrameMaker ExtendScript tech writers please take note that this sample needs t1.offset = 0; added or it only works one time.