Thanks, it works finally. But for someone else who also might want to change the pdf viewer I add: it it not sufficient to give in the path to the application package but to the application EXECutable itself, at least on Mac-OSX, in my case:/Applications/Skim.app/Contents/MacOS/Skim
Not true. I'm on Mac OS X and have been using "open -a skim" all along without problems and through several versions of LyX. It is not necessary to call the app's contents.
Cheers, -- Christian
