No, you can't add any bones / delete any bones.
Although, there is a solution for your problem.
What you can do, is use the skeleton from the model with the wings, delete the rest of the mesh apart from said wings. Import the mesh that you originally wanted to put the wings on, and then paint the bone influence on it

It's possible, because I've done it with loads of models... such as going from this:

To this:

I'm not sure if this is what you mean, but if it is.. the animations work perfectly xD
I use the latter as a mount
