If you change the authority on the library object it will not change the authority on the objects within the library. You will need to change the authority on the objects within the library separately – you can do this using the command GRTOBJAUT.
The basic differences between a data file and a source physical file are :-
1. The attributes on the file are different (PF-DTA or PF-SRC).
2. The internal definition of the files are different – a PF-SRC contains 3 fields (Sequence number, Change Date and a Data field), a PF-DTA file can contain any number of fields but should contain at least one field.
3. A PF-DTA can be keyed, whereas a PF-SRC is never keyed (it is however possible to build a keyed logical on a PF-SRC).
I’m sure someone else can tell you more differences, but I think these are the main ones.