You can't target untargetable mobs with our compile (unless you override it). Core release doesn't block it, but ours does.
As far as making any other plugin act the same way, yeah that's doable, and I could add it to spawnmaster (with an option to disable it of course).
For exceptions to /tar range, those exceptions are easily testable. In order to break the theory of them busting people (or at least flagging for review / watch), all they would need to do is check your loc, new target loc, and are there any valid exceptions (group member, pet, etc.).
AFAIK, based on our convos, once this is active, we won't 'nerf' it - it would just likely be default, but of course, would need to be tuned for proper range, LOS, clipping plane, various exceptions, all that. It would also be able to be changed via /mqrange (that's in our wiki, although I tured it to default unlimited like a couple years ago).
Don't worry about us sticking you with a nerfed down version - how you 'cheat' is up to you. My 2c.
htw