I photograph crafts I've made and turn them into collages to share online. Usually I accomplish this by unlocking the background layer on one photo and copying all the other photos into the same document, then mushing them around till I have a nice display.
Using this method I've essentially gotten rid of my background layer, which leaves me with a transparent background. I can throw a new solid fill layer back there, but resizing the canvas doesn't fill in the edges of this new layer like a background layer would, requiring me to re-fill it.
Is there a way to mark / make a new layer as a background layer so that it retains the properties of a default Photoshop background layer?
I am on a Windows computer if this is something that involves keyboard shortcuts.
Note: I know the described workflow is horrible but this was the easiest way I could think of to illustrate this scenario. I'm not looking for better workflows. I specifically want to know if I can create a default background layer.