Yes, OSConfig handles Theme Customizations. If you have a look in the OSConfig.log at C:\Windows\OSConfig\Logs you will see that OSConfig has been waiting this whole time for you to give it Theme Customizations all along.
The first file that OSConfig looks for is C:\Windows\OSConfig\Theme\Install.cmd. I can use this to do anything Theme related, like deleting default Wallpaper or default Themes. I’ll place this file at OSConfig\Windows 10\Theme\Install.cmd on my Deployment Share
I can then customize Aero.theme and place this file at OSConfig\Windows 10\Theme\Themes\Aero.theme
For Wallpaper I will create in OSConfig\Windows 10\Theme\Wallpaper the following files:
If you want to customize User Account Pictures, then place your custom files at OSConfig\Windows 10\Theme\User Account Pictures
And finally in OSConfig\Windows 10\Theme\Start I will place a LayoutModificationx86.xml and LayoutModificationx64.xml for my Start Configuration
And once I reboot . . . things look much better. No more Windows 10 Hero Wallpaper, and Start is configured the way I want it.
Lock Screen looks good
And the Login Screen as well
My OSConfig.log will detail every change that was made by simply adding the files where they need to be . . .