I recently re-tested this and found that it's working now. So I would like to retract my previous comment about it crashing. It DID crash but it may have been due to conflicts with other mods.
Anyway, this is a great mod and the only one of its kind that I know of. Really gives you the experience of playing out an alien invasion! If only Rockstar had included something like this is an NPC/AI event in the rural desert areas!
(Use Skin Selector and play as downloaded alien models with this mod for that extra effect!)