Flash MX 2004.
frame.labelType
Property; a string that specifies the type of Frame name. Acceptable values are "none", "name", "comment", and "anchor". Setting a label to "none" clears the frame.name property.
The following example sets the name of the first frame in the top layer to "First Frame" and then sets its label to"comment":
fl.getDocumentDOM().getTimeline().layers[0].frames[0].name = 'First Frame';
fl.getDocumentDOM().getTimeline().layers[0].frames[0].labelType = 'comment';