I understand what you are trying, to make changing the WP config settings more convenient but I do not think it is possible to change them from a plugin.
Constants like WP_DEBUG and DISALLOW_FILE_EDIT are defined in core files, specifically in
wp-config.php, according to the Codex and, looking over the source code of this file and related files, I could not find any hooks to affect their definition.
And, in PHP, once constants are set they can no longer be changed during execution. Their value cannot be changed and they cannot be unset. Attempting to redefine or unset a constant will result in an error.
Here is a small quote from the PHP manual on constants:
As the name suggests, that value cannot change during the execution of the script
If there are no hooks to affect the definition of these constants and if they cannot be unset, then I do not see a way around this. Editing the
wp-config.php file seems to be the only way to change the settings.