Setting up for both Steam AND Non-Steam?

I’d like to create build targets that allow me to “swap” between building with OnlineSubsystemSteam support, and building with the typical OnlineSubsystemNull. Basically, during development, I’d like to be testing network code directly within the editor (on one machine), and then switch to building the Steam-enabled target when I need to test it in Steam (on multiple machines).
IIRC, to properly test a Steam-enabled project, it needs to be packaged… so having a non-Steam build target seems like a decent way to avoid having to wait for building, packaging and deploying just to test changes to a single line of code.

Is this possible?

Here’s what I’ve tried:

This gives me the following error when generating project files:

The steam online subsystem is disabled in the editor, if you play in the editor it will fail to create the steam subsystem and instead fall back to the null subsystem. The effect is probably exactly what you want to achieve, test in the editor with null subsystem and packaged version use the steam subsystem. Besides you probably don’t need the online subsystem all that often while testing in the editor since you don’t really have to work with sessions unless you want to specifically test those.