Hi! If you haven’t been following <http://bugs.gnu.org/22039>, ‘guix system reconfigure’ is now able to dynamically load/start new system services, unless they are already running.
This works by talking to shepherd in a way similar to what ‘herd’ does, querying the list of current services and then dynamically loading new services in there (the interesting part ;-)). This is very conservative, so it shouldn’t bring your system down. :-) Errors in service definitions are caught when they are loaded. Anyway, if you notice something fishy, please report it, including info on the initial and target state of system services. Ludo’.