JWS, you can edit the provided ruby scripts freely. You can find them in the program directory under builtin_templates\export\bananalbum (this is under Windoze, I guess they are in a similar location for the Mac).
If you change the default script, I suggest you make a copy of the original files in a your own script directory (to enable your own script directory, specify a location for the "Location of user templates" on the "Files" tab of the preferences dialogue.)
Depending on what you want to achieve you'll need to understand quite a bit of the programming language ruby (and probably the way Bananalbum works).
Hope this helps,