Hmm, thinking a bit further, are you just suggesting registering the build as -3.7? What if I were to build the 3.6 branch? Would that overwrite my "real" 3.6 registry entries?

As things stand, the launcher can only register two copies of Python for any given minor version (one 32 bit and one 64 bit). So this would only really be useful for trunk (and for builds of versions where you don't already have the release version installed).