Is it possible to have a permanent Dual Modus?
No. I have not implemented anything like that.
Can you do this maybe?
Several people requested something like this in the past. But I rejected this idea. It is not clear how it should behave exactly and technically it would be complicated. It would mean that TotalFinder would have to be polling and every time when detecting there is missing dual mode it should be recreated somehow. Please note that Finder “browser” windows can come and go and this is outside of TotalFinder’s control. TotalFinder only reacts on Finder windows being created and “adopts” them as needed.
There is a Finder replacement app (not a Finder add-on) called Commander One if you want a permanent dual-pane.