Решение:
function TaskBarAddIcon(hWindow: THandle; ID: Cardinal; ICON: hicon;
CallbackMessage: Cardinal; Tip: String): boolean;
var
NID: TNotifyIconData;
begin
FillChar(NID, SizeOf(TNotifyIconData), 0);
with NID do begin
cbSize := SizeOf(TNotifyIconData);
Wnd := hWindow;
uID := ID;
uFlags := NIF_MESSAGE or NIF_ICON or NIF_TIP;
uCallbackMessage := CallbackMessage;
hIcon := Icon;
if Length(Tip) > 63 then SetLength(Tip, 63);
StrPCopy(szTip, Tip);
end;
Result := Shell_NotifyIcon(NIM_ADD, @NID);
end;
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Примечание
В uses необходимо добавить ShellAPI.