I wouldn't suggest messing with those. After all how long are they visible, a few seconds a week maybe! But if you must and some people do, take a look through this site. There should be plenty in there to keep you busy:
I think they call that a logon screen I use them you might want to install safe mode first that comes with your operating system.Here is link you can get logons here and down load the program you will need.https://www.wincustomize.com/skins.asp?library=26
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