Hello!
(maybe offtopic in this section)

I like the concept of "activities" and their posibility of binding windows to multiple desktop activities.
But i am missing a fast way to reorganize a bunch of windows to another activity.

ATM i've to use that way:
1. window-menu -> activities -> select "new-activity"
(now, the windows is bound to both, current and new, activity)
2. window-menu -> activities -> unselect "old- ctivity"
(now, windows is bound only to "new-activity" and out of my way )

doing so is somewhat ineffictive and time consuming in comparison to i.e. moving windows around the desktops.

so, is there a more comfortable way to reorganise window-bindings "with a prank" ?

You could use a KWin script to move windows to different activities.

Thats a quick&dirty hack, same as suggesting to use a script for moving windows between desktops instead of implementing proper gui functionality.

Unfortunately it is quite difficult to write "Proper GUI functionality" in this case, because one needs to specify the windows affected as well as the destination activity. KWin Scripting is therefore the appropriate mechanism to use in this case.