Different Airline Transit in Beijing

Hi, I am a Swiss National living in Seoul. I plan on travelling to Hong Kong for a couple nights, then Beijing for 3 nights, with Cathay Pacific. After that, I plan on flying back to Seoul, but with a different Airline. If I book both tickets in advance, will I still be eligible for the 72-Hour Transit Visa, even though I will be arriving and leaving with different airlines?

Also, I saw that you have to register with the police or at the hotel you are staying at. During my stay in Beijing however, I was planning on staying with a friend, so I won't be checking into a hotel. Will I have to register at the police station then?

Thanks.