Nope. If two writes happen concurrently on different fields you'll lose one write, unless you lock. The storage layer just stores the data as a blob that gets overwritten every time, it doesn't support partial updates.
i have the same sentiment, and for me systemd was getting so slow and hard to tshoot (the tools to analyze boot graphs and sequence showed service sequence breakage, some times there is no problem, sometimes sequence changed and problem happened) and i just changed for another distro without systemd and boom, startup in seconds no problem at all.
the creator even acknowledged the risk in the sample... but i do not understand why not create a more secure sample first time? since people will absolutely copy to test.