Mentioning ‘no root’ keeps it simple and welcoming for beginners while still addressing the concern. And no, this is not for Mac.
It works partially with Flatpaks on XFCE (or any desktop)
It can change the icon for the Flatpak launcher that appears in your menu. It edits the user .desktop file that Flatpak generates (usually in ~/.local/share/applications/).
However, Flatpaks are sandboxed, so changing the icon inside the Flatpak itself (what you see when the app is running) is not possible with this tool — that would require modifying the Flatpak bundle.
So: menu/panel icon = yes. In-app icon = no.
It should work with most window managers, but with some limitations. kAppIcon edits user-level .desktop files and installs icons into your personal ~/.local/share/icons/hicolor theme. This is the standard freedesktop way, so it works on any desktop/WM that respects the spec (most do).
However: The GUI is built with PyQt6, so you need a working Qt6 environment (works fine on Wayland too). Some features like automatic icon cache refresh or menu updates depend on the desktop environment (Plasma does it best, but it also runs gtk-update-icon-cache for GTK-based setups).
On pure minimal WMs (i3, Hyprland, etc.) it will still apply the icons, but you may need to restart your menu/panel or run update-desktop-database manually sometimes. If you test it, let me know how it goes.
The only “AI” involved was occasional use of GitHub Copilot for trivial autocomplete/suggestions, the same way many developers use it for boilerplate. All architecture, features, UI design, and logic are 100% human-made.
Unfortunately that’s not possible with this tool (and not really recommended). Flatpaks are sandboxed and their bundles are read-only by design. Modifying them directly would break the sandbox and cause update problems. What kAppIcon can do is change the launcher icon that appears in your menu and panel for the Flatpak, that works fine. If you want to change the icon inside the running Flatpak app, you’d need a different approach (like runtime overrides or repackaging the Flatpak), which is outside the scope of this tool.