[DiapDealer]

I've no clue, unfortunately, where the best place to set a calibre custom column in this plugin would be. This plugin's codebase is something that I have to re-familiarize myself with whenever a Calibre update makes it necessary to revisit it. Plus... other than inserting an extracted epub/pdf back into the calibre library, I don't have a lot of interest in adding much in the way of calibre-specific features to this plugin. I'm not all that familiar with calibre's codebase--and utterly clueless when it comes to setting custom columns programmatically. Happy to consider incorporating a patch or pull-request if you (or someone else) get something non-invasive working, though.

As for what type of mobi it is before unpacking: the options available in the KindleUnpack menu should tell you that (with individual books). If there is no ability to split, or extract an Epub (or pdf), it's a plain-jane Mobi-7. If the option to extract an epub is present, it's a KF8. If the option to split is present, it's a combination Mobi7/KF8. If the option to extract a pdf is present, it's an azw4.

But I'm afraid modifying this plugin to merely mark books for later unpacking isn't very likely. Perhaps a new "What's My Mobi" type of plugin would be more suitable for that. This one is very much geared toward extracting or unpacking from the get-go, rather than just flagging