Select only border of object (x pixels)

[Darty]

I'm have several pairs of images, where 1 of each pair is damaged.
I want to replace this with areas from the second image.
Do note: The color/brightness and zooming of the second image is slightly different.
What I do:
1: Try to match the contrast/color accordingly;
2: Create a new layer and delete the damaged spots.
3: merge them nicely.
And there is the small problem. Feather doesn't do the job, as the zooming is a little off.
Using Gaussian Blur does the trick, but I (have to?) manually select the border everywhere to apply this effect, unlike Feather.
The images are big, so it takes me a lot of time to do this manually and equally everywhere.

Is there some way I can use the blur effects on transparent edges automatically (like the feather plugins),
or can I easily select just x pixels from the border all around the object, to apply the blur effect on (like invert selection, but only for the border, x pixels)?

Edited April 8, 2017 by Darty

[Eli]

There is an effect that may help you : TR's Edge Fader Extreme Fader

[Darty]

6 hours ago, Eli said:

There is an effect that may help you : TR's Edge Fader Extreme Fader

That actually works pretty well to mix op the layers.
Did some tests with different settings and it's able to hide the differences in zoom, where many objects/lines on picture are broken.
This will save lots of manual selecting/blurring... Thanks!