The problem, and a very big problem, is that there's been no report here of anyone actually doing this. It's all theoretical.
Myself, I would be reluctant to say I was flying out of Guangzhou on the entry documents if I was in fact departing by ferry at Shekou. We really don't know how the computer systems tie everything together.
If you do it and it actually works, let us know.
Okay. I have thought of one surefire way for
Nabi to procure a ferry ticket in advance, which I was reluctant to suggest previously because I assumed there was probably an online booking channel. Without further ado, here goes: a friend of a friend runs a WeChat OA that is basically a concierge/handyman service targeted towards foreigners (e.g. English menus for everything). Coincidentally, they just happen to be based in Shekou, but it wouldn't matter because they are good at finding resources throughout China. Anyway, their account id is ringyringy. I've used them for a few random things in the past, and they charged me a flat service fee of Y50 per fulfilled request, which I assume is standard (I didn't inquire further or negotiate).