gnus-select-group-hook

gnus-select-group-hook is a variable defined in `gnus-sum.el'.
Its value is

nil

• This variable may be risky if used as a file-local variable.

Documentation:
*A hook called when a newsgroup is selected.

If you'd like to simplify subjects like the
`gnus-summary-next-same-subject' command does, you can use the
following hook:

(add-hook gnus-select-group-hook
(lambda ()
(mapcar (lambda (header)
(mail-header-set-subject
header
(gnus-simplify-subject
(mail-header-subject header) 're-only)))
gnus-newsgroup-headers)))

You can customize this variable.