Enhancing `modify-services' to support name in addition to type

[Brice Waegeneire]

Hello,

I was thinking of improving `modify-services' by adding the ability to
specify a service to modify based on it's name and not just it's type. 
This
would allow us to modify singleton services like the ones returned by
`simple-service'. I'm not sure if that's a good idea, that's why I 
prefer
to ask before starting to write a patch. Following is an example of how 
it
would like when modifying `set-xorg-configuration':

--8<---------------cut here---------------start------------->8---
(define t430-xorg-extra-config "
Section \"InputClass\"
  Identifier \"touchpad\"
  Driver \"synaptics\"
  Option \"HorizTwoFingerScroll\" \"on\"
EndSection")

(define t430-services
  (modify-services workstation-services
    ('set-xorg-configuration
     config => (xorg-configuration
                (inherit config)
                (extra-config (list t430-xorg-extra-config))))))
--8<---------------cut here---------------end--------------->8---

Brice.