Circumnavigate WP DISALLOW_FILE_EDITS.php

<?php
// Get the following into a theme or plugin, and WordPress will behave as if DISALLOW_FILE_EDITS is set to false instead of true.
// Hooks WP capability system to override the do_not_allow signal.

function __wpide_override_fsmethod( $caps, $cap, $user_id, $args ) {
	if ( in_array( $cap, array( 'edit_themes', 'edit_files', 'edit_plugins' ) ) ) {
		array_pop( $caps );
		$caps[] = $cap;
	}

	return $caps;
}
add_filter( 'map_meta_cap', '__wpide_override_fsmethod', 10, 4 );