Hi,

please do not invoke programs like 

  glib-compile-schemas
  update-desktop-database
  update-icon-cache

in individual packages.

The reason is that we are trying to keep packages modular.

If you add an icon cache with some fixed name that will cache just the icons
of that package in two packages, installing those into the same profile will
create a profile merge conflict.

We have profile hooks that will do glib-compile-schemas,
update-desktop-database and update-icon-cache anyway (in guix/profiles.scm),
so all that is required to do is to disable the invocation of these
programs in your package.