"it would be nice it they could be moved around (up/down either singly or multiple) to
change the "join" order."
I already think about it but this needs a lots of other work due it is not only move up/down the visible entry but any user added options as well as added metadatas etc... which are specific to each files have to be moved with them. I expect having it ready into a future build
Currently, just add files to be joined in the order you would have them in the process list.
Cheers
Remy