lispmacs[work]: You can define rules under 'define udev-service-type' ie (define udev-service-type (service-type (name 'udev) (extensions (list (service-extension shepherd-root-service-type udev-shepherd-service))) (compose concatenate) ;concatenate the list of rules (extend (lambda (config rules) (match config (($ udev initial-rules) (udev-configuration (udev udev) ;the udev package to use (rules (append initial-rules rules)))))))))