A Rookie Question regarding Prize Regulations

[Indagator]

Hi all, I'm a rookie U-boat driver playing with GWX 3.0. I apologize if this has been answered elsewhere, but my google-fu has failed me.

Anyway, I'm about to begin my 3rd patrol (2nd war patrol) in September 1939. I'm trying to follow the prize regulations, which I understand to last until December. However, I have a couple questions about what that entails:

1) Assuming I don't blast a passenger ship or neutral vessel, is there any consequence in game for torpedoing a lone enemy ship without warning?

2) Is there any way in game to give a warning to enemy merchants before attacking? In my very first war patrol I thought to get around this by firing a shot with my deck gun before proceeding to sink the vessel in any way I felt like it. But since that patrol ran afoul of a destroyer in the channel, and thus never made it back to base, I don't know if that would work or not.

Thanks guys. Fair winds and smooth seas!