You will want to look into the position of the 'enemy' mc. If it is on root you will be able to call it through _root.enemy if it is in another movieclip you will have to call it through something more like _root.OTHERMC.enemy. In short yes, you can tell another mc to change its frame, you just have to make sure that all the instance names match up to create the path to the mc you are wanting to edit.
Also make sure that you are placing _root in front of the MC location. If you have 2 mcs on the main stage frame 1 and have one named 'a' and the other named 'b' and b having these actions:
CODE
onClipEvent(enterFrame){
a._alpha -= 1;
}
Nothing happens, but if you have this instead:
CODE
onClipEvent(enterFrame){
_root.a._alpha -= 1;
}
It works.
That is because when you have just the
a._alpha it is looking inside of mc 'b' for mc 'a' and not in root for mc 'a' which means that it finds nothing unless you put it there.
Hope that makes since

and sorry it took so long for me to get back to you.