I get your points and that’s a valid issue however, systemd-networkd is designed for more persistent configurations but you’ve a few options:

1. systemctl reload systemd-networkd and networkctl reload. Don’t forget that if you change units on the filesystem a systemctl daemon-reload is required before the previous commands.

2. networkctl commands such as reload, reconfigure, up, down and renew. Read more about them here.

3. Temporary / volatile runtime units: manually drop a config under /run/systemd/network/ it will apply until you reboot the machine.

4. Transient scope units: those are kind of supersede temporary units as they are managed through a D-Bus interface so 3rd party interface can manage systemd. They don’t seem to work right now for network, but they might eventually do and this allows you to change options dynamically like they do for standard services.

An interesting thing to consider is that in most cases you can have your network configurations in /etc/systemd/network but only bring them online when required. This for me seems to solve most cases, you’ve your network all configured and ready to go.