That just gets into some of the card interaction rules you always have to remember.
- “Can’t” always wins. In a “can’t” vs. “must” situation, you’re prevented from doing the “must”.
- When “must” meets an additional cost, you can decline the additional cost to avoid the “must”. You must steal an agenda you access, but if it’s NAPD you can decline to steal. If you’re playing Haarpsichord with Red Herrings, stick them on the agenda you least want the runner to steal, not the one you expect them to go for first. And Mumbad Virtual Tour is a lot less useful in Gagarin once the Runner knows where it is.
2.1) In a “must either… or” situation, if you decline one due to an additional cost, you still have to take the other. If you play Emergency Activation Orders on Archer, the corp can’t say “I’ll choose to rez but, oops, additional cost, I’ll decline that and nothing happens”. Bye bye, Archer.