I recall one could use the Windows API to obtain a certain window handle, then pass it along with the desired coordinates to a function (SetWindowPos()?) that would move it to the desired coordinates; also setting size and other parameters was (is?) possible. Under Linux one would use the X11 API to do more or less the same. Not sure under Wayland but I'd be surprised if it wasn't possible with that as well.

You mean first let the WM position the window, and then use the X11 API to reposition the window somewhere else? Yes, I'm sure that's possible, but it might give some visual side-effects and may confuse the WM.

It's not possible under Wayland. Windows can't even position themselves, let alone have another process move them.