I don't have your rules or know exactly what your policy is, but I did a quick test of how to conver ToUpper in an event.
You'll have to find how to best implement in your policy.
I just took a string and converted it with these events.
Rule Criteria: Always
Set Authentication.UserName = String.ReplaceAllMatches (Authentication.UserName, regex((.*)), "\U\1")
When I rule traced them, i saw positive results.
String.ReplaceAllMatches(Authentication.UserName, regex((.*)), "\U\1") EELSASSER
You can probably do something similar with your policy.
You can also put in \L for lower case instead.