is it possible to replace face of a humanoid model with a plane face object? i have a 3d alien, i made it's body using adobe Fuze, and then i replaced it's head and feet with an alien model, now i want to replace it's face with a cute face that i just made, but the face that i want to use is a plane object and is not shaped like a face from the side views. i tried the techniques that someone in this website taught me to replace the feet and head but i couldn't make it, I'm wonder if it's even possible to do that?

here's a picture of the model and the face, but don't worry about the eye balls of the plane face, if i be able to put it on the alien's head, I'll handle the eye balls myself, they're separated objects.
Thank you for stating your problem clearly.
Yes, there is a way to do the lazy way (but will only get you half way there).
Position your FLAT face directly in front of your ALIEN head.
Select your flat face and press CTRL+3 this will give it a lot of subdivisions.
APPLY this modifier to the FLAT face.

Now, press CTRL+A to APPLY all your transformations both for the alien and the flat face.
Select the FLAT face, go to properties>modifiers>Deform>Shrink wrap. 
Select the ALIEN FACE as the object deformer and play with the X, Y, Z orientation parameters (by default should work immediately on Y).

Now you have conformed your increased polygonal flat face onto the surface of the alien's face like you wanted.

Thank you for voting me up as the answer for this question.

BFCT_Schiller