This extension offers a number of implementations for built-in functions (suffixed with "_ns") that allow GameMaker games to work with files outside of the "sandbox" directory.
The extension allows application to work with files anywhere where it could by usual rules (which is basically anything not in disc' root or other UAC-protected locations).
The extension also has full support for foreign characters in paths and files, and offers tools to convert between codepages if needed.
A demo is available at itch.io: https://yellowafterlife.itch.io/gamemaker-nsfs
A list of supported functions and documentations is available at http://yal.cc/r/17/nsfs/
While certain functions cannot be implemented for technical reasons, the issue can be bypassed by simply using file_copy_ns\file_move_ns to copy files in/out of sandbox for those operations.
Currently Windows-only. Given demand, Mac and Linux will be supported in future.