Best practices for scaling already executed insertions in 3D

[banana]

Hi,
I was just wondering, if there is a more efficient way to do this, than the one I know of.
Example: I have modeled this incredible window frame, which has some depth (meaning it is not 2D).
Lookin’ like this:

Now, how do I scale the inner part of the frame evenly inwards (meaning keeping the same distance to the outer part).
It should more or less look like this:

In other words: In a way I’d like to touch the insertion once again to adjust it. When it is 2D it is no problem, you can do so by using Alt+S. But when the frame is yet 3D, Alt+S messes up the whole model, because of the reoriented edge normals.
In my example I’ve used the Move Edge Funtion from the Edit Mesh Tools Plugin, but this required a multistep process. You have to do it on both inner edges successively. In other situations I’ve used Nulls in each croner as helper objects to snap to. Everything not really efficient.

Can you give me some advice on how you do this? Are there functions I do not know about yet? What are your best practices in these situations?

Thanks

[fave_edge]

ALT + S should do the job.

Maybe your face orientation is messed up. Or you forgot to apply scale.

[Okidoki]

Oh yes… Thanks… i always forget about Transform → Shrink/Flatten… was going to suggest extrude along normal and deleteing the inner loop…

[banana]

Alt + S really does it. Donnow why it didn’t worked until now. I’ve really seem to messed up the normals in my other models. Kinda embarassing for me now
Anyways… Thank you!