Win32: Reloading theme after theme-related registry changes? - windows

Question

There's a couple theming related registry keys that I'm editing through a personal tool:
HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\Themes\Personalize\AppsUseLightTheme (to change light/dark mode preference)
HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\Accent\AccentPalette (to change taskbar color)
I'd really like to update the theme appearance on the fly, but the problem is these changes don't take effect until after restart. The "Theme Settings" in the native System Settings edits the same registry keys, but also manages to update the color of the taskbar etc on the fly.
To understand how the native System Settings is reloading the theme, I've tried monitoring the outgoing window messages in Spy++ and inspecting the API calls in WinDbg. It broadcasts WM_DWMCOLORIZATIONCOLORCHANGED and WM_SETTINGCHANGE (with "ImmersiveColorSet"). But attempting to do the same doesn't seem to have any effect whatsoever:
fn reload_theme() -> Result<()> {
unsafe {
// Send message to all top-level windows.
let broadcast_handle = HWND(0xffff);
SendNotifyMessageW(
broadcast_handle,
WM_DWMCOLORIZATIONCOLORCHANGED,
WPARAM(3812725153), // Arbitrary value
LPARAM(1), // Arbitrary value
);
SendNotifyMessageW(
broadcast_handle,
WM_SETTINGCHANGE,
WPARAM(0),
LPARAM(w!("ImmersiveColorSet").as_ptr() as isize), // Equivalent to L"ImmersiveColorSet" in c++
);
Ok(())
}
}
One other discovery so far is that always updating the key HKCU\SOFTWARE\Microsoft\Windows\DWM\AccentColor causes a reload. There are still elements here and there that don't update though.
How can you "reload" the Windows theme without restarting after theme-related registry changes?