I was once able to change the placeholder ad banner on wlm with Messeger Plus! but i don’t remember how.
it’s like an (.dll) file?
You can’t change all of the assets on CustomizerGod, It’s with Messenger Plus! but i don’t remember where’s the theming tutorial.
Download Resource Hacker, open msnmsgr.exe and search on the files. One of it are the banner. Just replace it.