What is the fastest way to add a poly frame to a window hole? I am proceeding like this: first I select the hole external edges.

And I make a face out of them:

Then I duplicate the face in the Y axis, and delete the old one (I don't know how to detach the new face from the main object):

Then I extrude:

Then I extrude again all faces, so to inflate the box by the right amount:

Then I delete the back face:

Then I bring the open box to intersect the wall:

Then I make FACE - INTERSECT (BOOLEAN):

Then I merge the exceeding vertexes and assign the new material:

Et voilá: frame in the wall.
I am sure this is a stupidly long and convoluted process and that there's a quick command to do this.
Please tell me it's true.
Edit: a little bit faster.
Take the 4 sides of the window, duplicate and move locally in axis, extrude along normals with negative value, delete faces in excess, then move the 4 polygons back into the wall and do the intersect boolean.
It's a bit faster. Still makes no sense.
Use the Inset tool in Outset mode. Then extrude and delete the inner face.
Outset will create new faces around the selected face.

Avoid using booleans, they will create bad topology.