Restart systemd service *without* restarting dependents

I have four systemd services: {a,b,c,d}.service. d.service is the "main" service, and it is the one that parses the configuration file for all four. Typically, the four are started together. To make it easier to apply configuration changes, I have marked {a,b,c}.service as PartOf=d.service in their unit files. That way, when I restart d.service, the configuration changes are applied across all four services. However, there are circumstances (debugging, for example) where I want to **only** restart d.service without affecting {a,b,c}.service. Is there a way for me to do this, either through options for the systemctl restart command or through unit file configurations? I could also, I suppose, make a wrapper service - e.service - that contains {a,b,c,d}.service and then restart that when I want to apply config changes. I wanted to see if there was a way to do this without adding a fifth service, though. This is perhaps a misuse of systemd, and I'll gladly take recommendations for ways that I can structure this configuration better.