Is there a way to actuate rotators/pistons without controlling the craft?

@sflanker I'll suggest it, thank you

That said, I think more proximity sensor capabilities is a great idea and you should definitely post this in the suggestions section of the site. It would be awesome if there were a Vizzy command to get a list of all the other craft within a certain range, and it would be awesome if non-controlled craft could continue to have and track targets. I look forward to unleashing artificial life satellite swarms and watching my GPU melt!

TLDR: not currently possible, if you are controlling an astronaut or another craft, and you want to cause something to happen on a craft you are not controlling, your best option is to select a part on the other craft and activate it.

Vizzy programs do continue to execute on crafts not currently controlled by the player, at least when the craft that is controlled by the player is in a certain range, although some things stop working such as locked headings IIRC (i.e. autopilot). There isn't a general purpose proximity sensor, however you can sense the position of both the current target for a craft, and a part in that craft (by id). Unfortunately one of the things that stops working when you are no longer in control of a craft is its ability to have & track a target. So while you can target astronauts and other craft from a craft with a proximity sensing Vizzy script, as soon as you take control of the astronaut or other craft the Vizzy script on the first craft forgets about the targeting. Also even though astronauts count as parts, as soon as they go EVA the craft loses the ability to get their position. So if you are approaching a craft with an EVA astronaut and you want a rotator on your craft to do something your easiest option is to just select that part and activate it. It might be possible to do complicated things by activating a trigger part (like a light), and then detecting that activation in a Vizzy script on the craft and manipulating other parts in complex ways, however I haven't tested this so I don't know exhaustively what does and doesn't work on the non-controlled craft.