/usr/share/budgie-desktop/keycontrol/custom-keys.d/ is in budgie-desktop-environment 0.9.9.
This file is owned by root:root, with mode 0o755.
..
/usr/share/budgie-desktop/keycontrol/custom-keys.d/disable-keybindings.dconf
/usr/share/budgie-desktop/keycontrol/custom-keys.d/gnome-screenshot-area-clipboard.dconf
/usr/share/budgie-desktop/keycontrol/custom-keys.d/gnome-screenshot-area.dconf
/usr/share/budgie-desktop/keycontrol/custom-keys.d/gnome-screenshot-clipboard.dconf
/usr/share/budgie-desktop/keycontrol/custom-keys.d/gnome-screenshot-window.dconf
/usr/share/budgie-desktop/keycontrol/custom-keys.d/gnome-screenshot.dconf
/usr/share/budgie-desktop/keycontrol/custom-keys.d/show-desktop.dconf
/usr/share/budgie-desktop/keycontrol/custom-keys.d/show-files.dconf
/usr/share/budgie-desktop/keycontrol/custom-keys.d/tilix-quake1.dconf
/usr/share/budgie-desktop/keycontrol/custom-keys.d/tilix-quake2.dconf
/usr/share/budgie-desktop/keycontrol/custom-keys.d/visualspace-left.dconf
/usr/share/budgie-desktop/keycontrol/custom-keys.d/visualspace-right.dconf
/usr/share/budgie-desktop/keycontrol/custom-keys.d/windowshuffler.dconf