So did it with no alterations to proportions (Degroff recipe) and I'm inclined to say my initial suspicion that the spice would bully the other ingredients was right. Still a decent drink but would probably be better if the Becherovka was touched down to 5ml or so.
Benedictine isn't nearly as intense in it's spiced notes, so if you're going to sub Becherovka you might wish to touch it down a bit in volume and make up the difference with perhaps a wee bit more triple sec. I like the idea though, might give it a shot this weekend.