Changing airports in Shanghai - still 72-hour transit permit?

Hello,

I'm a Finnish citizen, and on my return trip I'm flying from Taiwan to Finland via Shanghai. However, my first flight arrives at Shanghai Hongqiao airport and my second flight to Finland leaves at Shanghai Pudong airport (stay in total less than 24 hours), which means that I have to leave the airport to reach the second airport. Judging from your previous answers I should be able to do this without a transit visa, right?

However, I just called my airline to ask them about this and inform them about my intention to leave the airport, but they only replied that they cannot give permits to enter China. Maybe the officer wasn't fully aware of the procedure since she wasn't working at the airport. So, when I'll be doing my check-in in Taiwan and inform my airline about my intention to leave the airport in Shanghai, is it certain that they will know which form I have to fill in and what they should do in order to get me the permit at Shanghai Hongqiao? Or can I get the permit somehow after my arrival in Shanghai without cooperation from the side of the airline?

One more question - do I need to register at a police office even though I would only go from one airport to another one with a stay of 16,5 hours? I arrive at 5 pm and leave on the next day at 9 am, so I'm not sure if the police office is even open during night.

Thanks a lot for your answers!