Tried to add a conditional symbol in the Build Configuration for my project.
I always get an error relating to the format of the Package name, which is not changeable.
Also, is the conditional symbol usable within the C source code and B4R libraries?
No. However you can add #defines (and other stuff) by following these steps:
Open the installation folder and find a file named Defines-Template.h
Copy this file to <project>\Files
Edit the file and add whatever you need.
Now the IDE will use the custom template to create the B4RDefines.h file. This file is referenced from all libraries and modules.