Editing Core Libraries

In the .pioenvs folder I find only the header files (.h) but not the program files (.cpp, .c),
only for the user libs the program files are included → screenshot
So, I want to edit the core files of a project, to improve the core libraries. Can I do this theoretically
in the .pioenvs folder? If yes, can you extend the .pioenvs folder with the program files, maybe as an option? When not, an additional folder inside of the project folder like “lpc1768_core” or “arduino_core” with the core files for compiling were useful. This folder should not touch the original files of the framework and only the files needed for compiling should be there.

Hi @sstaub!
Please don’t modify files from environment directories .pioenvs they are temporary and may be overwritten after each build. Packages with source files are located in PlatformIO home directory: