No, not the actual tunnel width; they just added stuff (cables, equipment, etc.) that narrowed the clearance.
With all this talk of deinterlining Gold St. Iseemingly inspired by then deinterlining the IND uptown, one difference is that the uptown change basically consolidated operations, so that the and and and start and dinish in nearly the same places, and use the same yards on both ends. As far as the crews, each terminal on the branches are also consolidated into the same "section" or "district" (i.e. "North", "South"). With the BMT South, all have the same yard at one end (and the uses it too), and are in the same district, so it's already consolidated like that. (And the and are there too, but moving them around on that end won't really change anything in that regard).
I guess the sole benefit of these isdeas is trying to avoid the slowdowns where they come together at Gold St? I don't think that by itself is worth changing up the lines. For one, a lot of the delay is because it seems they now basically stop everybody at that interlocking to ask who they are (i.e. "spot"). They already had cameras there (at least southbound, when I used to be over there, 11 years ago), but it seems they don't even want to trust those anymore (and they even less trust punches). All of these "backup" measures, piled on top of one another!
They need a better way of the tower people knowing for sure what is what (it's already on the now computerized train registers), and also schedule it better so that trains trying to get to the same line (either way) aren;t arriving at the same time. (Which seemed to happan a lot).
It's nice to have direct access to different trunk lines on the outer branches. Also, on the uptown IND, one interlined service was rush hours only, while the other only served two local stops (weekdays only) and ended, so it wasn't as big a loss as what is being suggested for the entire BMT South.