Ok, so first, I was mystified at what was wanted, with a posting which had more words in the title than in the body. But, it appears Peter had some intuition for that, so…
Second, I don’t see a lot of value in the suggestion. Sure, it’s fine, but would I like to see devs spend their cycles on that? Nope, I have other ways to do that function, that exist right now. I want to see devs spend their time on increasing real text editing value added functions.
Third, opening a new instance of a running Notepad++ has some problems IIRC about saving any changed settings, or disabling backups, or some such.
That all being said, I do run a second instance (typically a close-to-virgin instance), to try out problems people bring up right here!
I create a Run menu item to run a current portable version using the -multiInst command-line parameter.