Is that like pasting the text into another app, change the case & paste the text back into the CB?

It isn't like it, it is it.

Would that overwrite the exitsing text?

No (unless you purposely overwrote the text).

And yes, it might be a (slightly) longer process, but IMO, it isn't worth it to add such a feature to the CB. I suppose I might be biased...I usually have an editor already open to use...