@cunei  I realize it may break, but I'm specifically relying on this feature. I have two competing requirements:

1. The default file should "just work" without any required command line arguments
2. The configuration should be overridable (as appropriate) when runnning in an external system (like the IDE uber-build).

As such I *want* the override behavior when the SBT_VERSION_PROPERTIES_FILE is set.  That's how we adapt this cookie-cutter definition for different branches/versions which are similar as well as allow customization by external scripts.

This is an aspect I've long debated the best mechanism for dbuild (as for sbt).  Thoughts/ideas welcome.  If you invert the semantics of this, we'll modify it then.  For now, I need that mechanism for this whole PR to hang together.