unfortunately not... As you might have noticed, gPapers had not seen any active development for quite some time before I started working on it this year, so there are still a number of rough edges.
I agree that changing the journal information should be possible from the "edit this paper" dialog, feel free to open a request at the issue tracker:
http://code.google.com/p/gpapers/issues/entryThat said, you can change journal information in the source pane in the top (right-click for edit). Also note that changing the bibtex information does not have any direct effect -- the bibtex information is only stored for convenience, e.g. for exporting it (which is not implemented yet) or just copy&pasting it somewhere else. There is a little workaround you could use, though: Edit the bibtex to your liking and then copy it into the "Import BibTex..." dialogue, this then generates a new entry with all the information from the BibTex.
Hope that helps, best
Marcel