Why not use a periodic force effect to pull/push units nearby? Give the unit a behaviour with a period of 1 frame (1/16 seconds) and a periodic effect of search area. This search area finds suitable units for push/pull and then applies a force effect on them. The force effect causes them to move.
Do note that this will likely scale very badly, even if a trigger solution was used. Although you may plan to allow an unlimited number, I would strongly recommend some sort of practical limit to prevent performance degradation.
You can use Galaxy script to register unit events to triggers dynamically. That might be able to achieve what you are after by registering new units as they are created. However this will not move them periodically, but only when they enter.
Use a chance based effect branch before the missile is launched. The non-miss branch lands the proper missile. The other fires a dummy missile that does no damage, makes "miss" when it impacts and targets the point of the attacked unit (not the attacked unit, so it appears to miss).
I am sorry but I do not have the required experience with actors to answer that. I imagine the only way would be to not lose the link or to use a non-actor system to control the actors (such as a behaviour or effect which at the required time will make a new actor on the involved unit while the old actor is removed via trigger script).
You could right-click and select "Save as", then reupload them somewhere and use the newly uploaded version.
I'm sorry for being pesky, it's just that I'm really looking forward to having your tutorials submitted at UDmod!