In the actual Windows Explorer, whenever you go to Properties for a file, you get a Properties Window. This window has controls which look like Labels (Static), but are actually read-only Text Boxes with no borders (Edit). So you can click on these, select text, copy it to the clipboard, etc.
Meanwhile, in Mp3tag, the properties window only has Labels (Static). You can not copy text out of these without using a special program.
I'd request that the Labels in the properties window be replaced with Read-Only Text Boxes with hidden borders, so they look just like the labels, but instead can have text copied out.
To edit tag data please use the the action, the extended tags dialogue, the converters, the web sources, the files list, the tag panel.
Especially the last two are already open and you don't have to call a special editor or program.
To be honest: as there are already so many ways to edit the tags, I hardly ever use the properties dialogue.
This is not necessarily for editing data, this for examining existing data (The Properties Window), and adding the ability to copy text (that you can read) to the clipboard. Would be useful for cases where you are unable to type international characters but they are in filenames.
You can already display the filename in the files list, you can import data from the filename with Convert>Filename-Tag, you can set the filename not only to be read-only but also to be modifiable in the files list.
In short: no need to use the properties dialogue.
I would use the function Convert>Filename-Tag to import data from the folder.
If the folder is also the current folder then you can copy from the folder-box in the tag panel.
If you need to copy from the filename, you can set value and field to %_filename% in the column definition.
To swap artist and title (and I hope we talk about the tag fields and not just the filename), there is a post in the FAQs: