Editing the *grep* buffer doesn't work, because text character key bindings are not defined (used to be bound to self-insert-command with previous Emacs versions).
No success with grep-edit-2.12 either. The "wgrep" fork at https://github.com/mhayashi1120/Emacs-wgrep/ seems to work, though.
# Ulrich Müller <ulm@gentoo.org> (24 Feb 2015) # Does not work with Emacs 24 or later. Last visible upstream # activity in 2010. Use app-emacs/wgrep as replacement. # Masked for removal in 30 days, bug 541234. app-emacs/grep-edit
Package removed.