100% not possible. There is no script, addon, plugin, whatever which makes this possible. Messenger is quite simply not build for that.
However, the idea of having multiple accounts running in one contactlist window has been very briefly talked about in one of the sessions between MVPs and the Messenger team this year at the MVP summit.
But seeing that they still don't even allow to run two Messenger programs at the same time, I wouldn't get my hopes up too high. Maybe they will make something like that in like 10 years time or so
And even running 1 account is not without its bugs as it is now... so yeah...
Another idea, which is more likely and which has come up in those same sessions too, is having a kind of tabbed contactlist window where you can easly switch between contactlists/accounts. But even that is just a 'wild' idea; So don't expect too much in the next couple of years.
Though, some 3rd party addon/tool did exist which simply executes two Messenger programs (polygamy/multi-messenger) and showing them both in a tabbed user interface window. Can't remember its name anymore. It was made by someone on this forum a long time ago as kind of an experiment IIRC, but I think there were also some problems with it.
Best thing you can do for now is simply allowing Messenger to run more than one instance (polygamy/multi-messenger) and switching between them via your Windows Taskbar. You could even group the two or more buttons together on the taskbar by enabling Windows' "group similar taskbar buttons together" option.
And while you're at it, you might wanna suggest this to the Messenger team yourself (use the menu
Help >
Send feedback). With stuff like this, if no-one requests it, it wont be made, so.... The more people ask for something, the more chance there is it will be made (if possible)....
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