Triggerhappy's method will almost work in a trigger, except for a few errors. The main problem is right here:
"_x setbehaviour "aware"" foreach
The second bold quote "closes" off the first one, which makes an error. Remember that you can use braces as quotes: {
{_x setbehaviour "aware"} foreach....
It's also not a good idea to use "east" as a variable name, because "east" is also a scripting command, and that is never a good idea to do. But you don't need the variable at all, just put this in a trigger, covering the whole mission area, activated by "east present" (and synchronized with something if you don't want it to happen at the beginning of the mission):
{_x setbehaviour "aware"} foreach list this
or
{_x setbehaviour "aware"} foreach thislist