I was so frustrated because I could not find any other addon than Discord Action Bars that supported the way I had set up my bars: bar1-5 showing all at the same time grouped on the right side on the bottom of my screen, so I had 5 rows of buttons and could click shift+1-5 to _delete_ the keybindings from bar1 and apply them to bar1-5.
So this is what Bartender2_BindingSwap does for Bartender2 (and possibly other bar addons, it is not really dependant on Bartender2); it adds 6 new keybindings: "Swap to bar 1-6", which when pressed will do exactly that.
There are no slash commands or configuration options besides the keybindings you have to set.
Mikma told me that I might have to code it so it works with shapeshifting and stancechanging. I haven't tried this myself yet but I assume it doesn't work very well. If someone wants to test that for me it would be great.