All of the answers here do address aspects of your question, albeit from different perspectives. I think you may be missing that the finer points of the answer are probably classified and not publicly available. You're also confusing the question of whether an aircraft is armed and whether its operators intend to use it to attack you.
As Jörg and TomMcW pointed out, the specific airframe or even general type - even assuming you can reliably identify it BVR - is not necessarily an indication of its belligerent or benign intentions. Even balloons have been used in "modern" warfare. Nothing in particular (other than cost and fear of having its legitimate civilian aircraft be targeted) would prevent a hostile force from packing say, a Gulfstream G650, with explosives and using it for kamikaze style attack. No military aircraft were used in the September 11 attacks, but that didn't prevent them from causing a great deal of destruction.
The closest answer to your technical question is probably Ralph J's, but as mentioned, the details are mostly classified (for obvious reasons). That being said, identifying key characteristics of the target aircraft is definitely possible BVR (with unknown, but likely fairly high reliability). Whether those characteristics are enough to clearly differentiate a combat aircraft from a civilian aircraft really depends on how your enemy defines "combat aircraft".
As to "how far out", that's likely not going to have a simple (non-probabilistic) answer. Target identification is generally based upon a fusion of data from multiple sensors with varying operating characteristics. The specific answer almost certainly depends upon a number of variables such as terrain, weather, the size and configuration of the aircraft, its flight profile, and aspect to target.