Which version of AE? I also do not see an attachment.
Thanks for the picture, but it's STILL tough to know what you're really after. "More realism and depth" means something to you, but not to everyone Some people actually WANT to add a third eye over a nose using AE, for example. Can you be more descriptive of what you want the viewer to see?
And I don't think I've ever seen a "Slip" tool in AE, either. You'll want to double-check for it's real name. Sorry.
The key to believable effects for me is always what the edges look like. Make great edges that blend seamlessly with good color correction and you are 90% of the way there. For your effect to work I would think that the face needs to distort then a tear or bulge appears where the other eyeball is going to be. The distortion continues and the face is warped out of shape allowing the new extra eyeball to morph to its final shape.
If your actor is moving their head around for the camera is moving you have additional problems to solve. Those can usually be handled with tracking or 3-D camera tracking. If the face turns from profile to fullface then you may need to do the project in a 3-D using photogrammetry to re-create the model of your actors face.
Let me know if you need more information on creating 3-D models from photographs.