I’ve found that
<app /> and
<source /> nodes are mandatory for root nmml project file. Even
<haxelib /> that includes openfl or lime is mandatory too to put default/icon.svg to the build.
So, in order to build bulk resources separate of main application I have to create dummy main class, that looks like clumsy workaround.
Is it possible to create a pair of project setup files, one of them to make clean build of assets (swfs, fonts etc.) and another one to pick libraries made earlier and include them into application bundle?
It’s quite impractical to rebuild all resources on every application run.