does it have this ability or is it just a GUI?

By default it is a GUI, basically a clone of Emplode, but there is a lesser know emptool clone in there as well. Try...

java -cp jemplode20.jar org.jempeg.empeg.emptool.Main

I haven't really used it since mschrag first wrote it, but it used to work just like emptool so any scripts that work with emptool could probably be tweaked to work with it as well.

-Mike