units that belong to neutral (and possibly not only) have a built in periodic command to go back to their spawn position. you can detect and override this command.
something like:
Unit - A unit Is issued an order targeting a point
conditions:
-> specified unit.
-> the point is in region x. (make region x at spawn location of that unit)
action -> order unit z to do y.
this should override the built in order to go home. however, I remember that when I did this there was still some funny behavior that I had to play around with since i'm not sure exactly what the conditions for the go home command are and how it works under the hood. so it might not be 100% foolproof.
another way to overide this that is worse in a lot of ways is to have a periodic trigger that reinforces the behavior of the unit you want, so that whenever the hardcoded command tells it to go home, you just tell it to keep doing what it was doing. since the hardcoded "go home" command only happens once every few seconds - your commands will win out. the only reason i state this even though it is a much uglier solution, is because this gave me an end result with no caveats. but this is much more resource heavy, and creates clashing commands that will give your unit some schizophrenic behavior instead of just replacing the original command. so, much less smooth - but was less prone to whims of the hidden hardcoded stuff.