That's unfortunate, and it's probably why I was originally advised to have separate copies of Calibre Portable if I wanted to open directly to the library of my choice.

I have Calibre Portable installed on an external hard drive with half a dozen different libraries, and I've never found it much of a hassle to switch. No file dialogues, just select the library from a list once Calibre is open. One question: do you have your different libraries in different locations? If you keep them all in the Calibre Portable folder, switching between them is trivial.

Fortunately, library-specific settings are saved in the library so these should be fine. If you run calibre.exe instead of calibre-portable.exe, you may find some oddities with settings if you move to a different computer, because it will save changes to the computer where you run it, not to the Calibre Portable folder. Either way, it seems to work now, so I might try to consolidate my two copies of portable Calibre back down into one. I hope that's what you meant, because I really have no intention of switching back to regular Calibre. Well, I got it to work changing the target file from calibre-portable.exe to calibre.exe which was one folder deeper.

Programs like calibre