> Did you call gnus-registry-initialize before evaluating your setq? I
> am not certain but I think this is necessary.

I doubled check yes it is, and even if I do describe variable I obtain

,----
| gnus-registry-marks is a variable defined in ‘gnus-registry.el’.
| Its value is
| ((Imp :char 105 :image "summary_important")
|  (Work :char 119 :image "summary_work")
|  (DONE :char 100 :image "summary_personal")
|  (TODO :char 116 :image "summary_todo")
|  (Later :char 108 :image "summary_later"))
| 
| Documentation:
| List of registry marks and their options.
| 
| ‘gnus-registry-mark-article’ will offer symbols from this list
| for completion.
| 
| Each entry must have a character to be useful for summary mode
| line display and for keyboard shortcuts.
| 
| Each entry must have an image string to be useful for visual
| display.
`----


but when I insert a registry gnus uses the official one, that is TO-DO
instead of TODO etc.  I am puzzled.

So the only solution was to copy the gnus-registry in my personal emacs
directory and modify it to my needs. That worked!

Uwe