Ebok,
I see where you're coming from.
If I'm reading you correctly, your objection to using "seize by force" in that kind of situation is that it's too effective/powerful, in comparison to Single Combat, right?
Although I don't particularly expect anyone to play the game that way, I find it odd that if you finagle a strategic goal - something you can seize - into a situation, then the outcome of the fight is weighted more heavily in your favour. That's an odd thing to consider, if you're playing and trying to decide which move is a better fit.
In the example situation we were describing, I'd take a position somewhere in-between what you're describing and simply ignoring the "take definite hold" clause altogether.
My own approach would NOT be to invent something additional to make the choice meaningful (like your examples of inventing a horn which can signal an alert), but I WOULD interrogate the fiction to see whether the choice matters, and make those details count. As a simple example, maybe "taking definite hold" means that you're past the (presumably dead) guard and launching yourself with initiative into the next room. (One way to look at this is to say that the MC move I would make next would be to offer the PC an opportunity.) Failing to "take definite hold" would be meaningfully different, in that I would choose a different move - perhaps the guard in the next room has time to barricade the door (or sound the alarm, as you suggest).
I can see some situations where no such options would be fictionally appropriate, however, and in those cases I'd be happy to simply let the PC have a 'free' victory in this sense - it's a testament to their luck and fortunate fictional positioning, and it should be allowed to stand.
It's a pretty subtle nuance in comparison to your approach, I think - just a very slightly different way to handle those outcomes from the MC's side.
Although I generally don't like using abstract "objects" for the "seize by force" move (like "seizing the moment"), in a case like this, I think it could be useful. Taking definite hold of the moment, or of initiative, of the situation, can be a useful guide to the MC in terms of deciding which move to make next and how to generally paint the situation.
That's why I dislike the "choose 1 on a miss" option in the new move: it seems to allow any PC willing to take harm, or heavily armoured, to automatically achieve strategic goals in a fight, without the roll mattering all that much. (Many PC-NPC matchups, and some PC-PC matchups, lead to an established harm of 0 on one side, and enough harm to kill the opponent on the other, which means that other choices are fairly meaningless - I don't need to suffer less harm when I've already got 2-armor, for instance. In the last four fights/battles I saw take place in my AW and Fallen Empires play, there was no harm at stake at all for the PCs, including one PC-on-PC fight.)
I can appreciate the "action movie" interpretation of this; perhaps it drives play more towards other concerns. "Sure, you can kill those guys. But is it worth it?" However, it leaves Apocalypse World feeling much less "real" to me, which makes it a less interesting game.
I still like how your hack, as presented here, balances Seize by Force nicely with Single Combat and potentially resolves that issue (or at least mitigates it).
I'll give some more thought to a different way of parsing Seize by Force vs. Single Combat...