To install/update the packages of the default profile, use

    guix package -m $MY_GUIX_MANIFESTS/main.scm

and for other profiles, use

    guix package -m $MY_GUIX_MANIFESTS/name.scm -p $MY_GUIX_PROFILES/name/name

where `name' is the name of the profile (e.g. `doc', `media', ...).