Modifying a variable from describe-variable

[Tom]

The other day I checked a variable with describe-variable (C-h v)
and I wanted to do a minor change (like changing a character) in
the value. It was a complicated variable with lots of
sublists (e.g. font-lock-keywords), so it would have been natural
and easy to change it on the spot in the *Help* buffer.

E.g. the user presses e (for edit) in the *Help* buffer which
either becomes writable or a new buffer pops up with the variable
value. The user modifies the value, presses C-c C-c and the
modifications are applied to the variable.

It does not seem hard to implement and it would be quite
convenient for quick experimenting with the value of some variable.

I checked the bindings (surely someone has thought of this
before), but I didn't find an existing function to do that.