Is there a faster alternative than `nixos-rebuild switch` when updating services?

Often I'm configuring a new service and having to run nixos-rebuild switch for the changes to take effect. For example setting up a configuration for a webserver. However the nixos-rebuild switch takes quite a few seconds to run. Is there a quicker alternative to rebuild just a subset of my Nixos configuration? I did notice a --fast parameter - however this does not seem to make much of any difference.