On my car, there's a connecting pipe between the breather hole on the tappet cover and the intake manifold. I haven't modified it for any purpose whatsoever.
If you block the breather at the tappet cover or oil sump, you'll pressurise the sump and engine damage may occur (due to blowing seals and leaking oil). If you leave it open, you'll have a film of oil all over your engine in a short time.
The intake manifold end is between the air cleaner and intake manifold. It shouldn't be allowed to breath open air as dust and dirt can enter the engine. If its blocked though, no harm shall be done.
In short, don't modify it at all! You'll damage your engine if you modify the pipe connecting the breather and the intake.