Hmmm. Late answer, but I think it depends. Not even on what kind of rules or crunch is added, but how much and how many different kinds?

Looking at the Designing New Games section of the Dream Askew/Dream Apart book, it actually addresses this at the end. It even gives some suggestions on how to add in new elements, advising that you need to remember that any changes will ripple through the whole design and so need to be thought out carefully to figure out how to make them integrate smoothly. But then it notes:

"The other thing to keep in mind is that as your game drifts farther from the line established by Dream Askew and Dream Apart, it’ll also be drifting closer to the design space of other games. And that’s great! That means you have new resources to contemplate and borrow from. Look to other games for ideas about how to execute your goals."

Even this isn't saying it'll become not a Belonging Outside Belonging game or that you can't call it that. But it does have a good point that you drift further away from BoB, and it does start becoming a little less that and a little more something else. I don't think there's a solid line where it would stop "counting" or you'd be absolutely wrong to call it that. Belonging Outside Belonging is, as the book says, "about marginalized groups establishing an independent community, just outside the boundaries of a dominant culture... [that has] a hopeful, precarious, vulnerable quality to them." I'd say that if there's a core quality your game might have to have to be BoB, it'd really just need to have that "hopeful, precarious, vulnerable, independent group creating their own space and coming together outside of larger society" element to it. But even then I'd argue that if your game had literally every other element but was just about a club at a college and didn't really separate the characters out from the rest of the school or town, it'd still be fair to call it that, since it's so 100% the BoB system.

But I feel like if you adjust multiple elements, add multiple things and take away other things and otherwise tweak it to greater degrees, it becomes fair to call it more its own system inspired by BoB/with BoB elements. I think if you make a game with a GM, or add in dice rolls, or change/take out tokens, or take out playbooks and shift to a different character creation system, I honestly think any of those changes individually wouldn't make it not Belonging Outside Belonging. Even a couple of them wouldn't. But if you tweak it so that it's a game with a GM, you create characters without playbooks and roll dice, and there are no tokens, I think it's changed enough in mechanics that "inspired by" becomes fairer to say. Which is very cool, because then it's kinda evolved into your own game system.

Vincent Baker is very on board with the fluidity of PbtA. He gladly lets people use PbtA to describe games that have no resemblance to Apocalypse World. And he's even said that his own non-AW games like Mobile Frame Zero Firebrands are PbtA games because they are building on game design theory first presented in Apocalypse World. I'm paraphrasing a bit, but he's pretty insistent that PbtA is a school of game theory and not a system. 

I have no idea if Avery Alder approaches Belonging Outside Belonging the same way? I haven't read Dream Askew, so I don't know if this specific thing is addressed in the book. Mx Kit has mentioned that there is talk about how you can change things but that's sort of different. Does Alder consider BoB to be a system? Or does she consider it another thesis on game design to be further developed and built on by community?

Either way, my favourite PbtA games are the ones that don't even remotely resemble Apocalypse World. Like Wizards Aren't Gentlemen for example is absolutely bloody fantastic. So yeh, make BoB games that don't resemble Dream Askew.