PDA message mechanics: sender code irrelevant?

[ZeWaka]

That won't help me hide my identity, or forge a conversation.

You can still change sender_name. This allows you to spoof 'who you are' essentially. You just need to send out messages on your packet sender rather than just replying normally.
Yes, it does 'fix' itself if you re-scan the names but not many people do that. It's easier to reply to a PDA message in the chat window rather than the PDA itself.

Example: if you don't enter an address, the message will be sent to all PDA's on a station, and that somehow results in a lot of angry responses. I think I need more help then the Wiki provides at this stage. Any tips?

The way I explain this is as follows: You send the message out on the frequency, but not to a specific PDA. That causes all the other PDAs to receive it because it might be intended for them. You can use this mechanic to build PDA chatrooms with the help of mechanic components.