how to add a film layer effect to an existing image

Again, you'd have to shoot both packages in the same orientation.

Then place the vac sealed image on a second layer over the opened package.

Next add a third layer to paint white using the second layer as a guide.

Hide the second layer after painting highlights.

Change your blend modes and opacity on the highlight layer to add them to the unsealed package.

This is a complete hack job with no visual reference but you get the idea.

The key to all of this is shooting both packages the same orientation so you can align them when stacking.

I thought of that too but wasnt sure if that misrepresented how the film really looks when applied to the product.

What if you shot the product with the film seal with intense lighting/highlights,  then removed the film, matched the position then reshoot the product?

You could overlay the film layer and adjust accordingly while being able to color correct the meat.

Even if you reposition, you should be able to align the sealed meat for an overlay.