Although BitRock InstallBuilder has a GUI, it is also practical to edit the sources, which are XML files, in an editor.
Beware that when you save the sources from the GUI, hand-edited files may be reorganised. For example, in many cases element siblings are rearranged into a sorted order. (Also beware that hand-edited files are not automatically re-loaded by the GUI; you must do this explicitly.)
Here I make some suggestions for trying to keep BitRock sources readable.