Pythagoras
How to Change Skins in Minecraft: Education Edition (Windows)
Updated: Jun 30, 2021
What's gonna happen: you'll open up the file holding the skins for Alex and Steve and replace your skin for either Alex or Steve (depending on slim vs classic size)
I am not responsible for anything breaking or being weird
(I have a feeling there is a shortcut for this but I don't know that way at the moment)
Open a file folder in your computer
Confirm the Navigation Pane is open
Click "View" > "Navigation pane" (on the left)
"Navigation pane" should be checked
Enable viewing of hidden items
Click "View"
"Hidden items" (on the right) should be checked
Get to the skins file
In the Navigation Pane, click "This PC"
Open your local disk, "Name (C:)"
Open "Program Files (x86)" > "Microsoft Studios" > "Minecraft Education Edition" > "data" > "skin_packs"
Open "vanilla"
You should see three text/json files and three image files
The text/json files cannot be modified
Open the folder with the custom skin file, should be a png
Move/copy "custom skin" into the vanilla folder
If your new skin is Slim
Rename "alex" to "alex_original"
Rename "new skin file" to "alex"
If your skin is Classic
Rename "steve" to "steve_original"
Rename "new skin file" to "steve"
Open MC: EE and change into your custom skin
Why does this work? Because in the skins text file, the texture for each is the png file. By renaming the custom skin to one that is already in the text file, your skin will be the image that is referenced.

Why does this work? Because in the skins text file, the texture for each is the png file. By renaming the custom skin to one that is already in the text file, your skin will be the image that is referenced.
You can use these steps to use more custom skins - instead of "vanilla" go into "edu" and then a set of skins. Rename your custom skin into one of the skins shown. Rename the old skin into something else.