Ref: Background to my issue is in post titled '
File not empty error' posted July 20, 2017 (Caution: it's wordy. Read only if completely confused with this post.).
In short, when installing Calibre in new computer, it created the default-folder "Calibre Library". I created a new folder in order to import my books called "Calibre-Library" (with a dash).
Transfer went perfectly.
Now, due to some latent OCD tendencies, I want my current (new) folder to be named 'Calibre Library' like the original default. And to delete the original folder.
So what I figured I would do is as follows:
1. Rename default folder from 'Calibre Library' to Junky Library
2. Rename NEW folder from 'Calibre-Library' to 'Calibre Library'
3. Delete Junky Library
Simple and logical - except that I can't do it.
While Calibre is obviously recognizing that I have the two libraries (I have the rename option), it only allows me to 'see' the new library (Calibre-Library) in the options. It looks like as far as Calibre is concerned, the original default-folder-library doesn't exist. Except, thanks to @BetterRed's comments, I know it does since the option to 'rename' does exist (evidently option not present with a single library).
So my question... can I rename the default-folder through File Explorer so that I can properly rename new-folder through Calibre? And then delete default-folder through Explorer again. Would I be messing something up in Calibre by doing that?
(Yeah... I'm sorry about this post. This has all the makings of an Abbott & Costello routine

I honestly tried to figure it out on my own. )