I build classicals and use more BRW than any other wood. Brazilian Rosewood while haveing a wonderful tone can sometimes crack if you look at it the wrong way

.
If it is just starting to open and is not a big gap the best thing to do is to apply a clamp to help close the crack but leave it snug not tight. You do not want to cause the wood to deflect, just help to close the crack so that when you wick in the CA that it will not have an unseamly crack. If you do this (mostly closing the crack) it will be very close to indistinguishable.
Additionally if you see any hairline cracks that have not opened it is a good idea to stop additional cracking by applying some CA to that crack.
I do the above before I thickness the plates and afterwards it is difficult to find any deflects. For tight cracks I use CA whereas for loose knots, voids and other imperfections where filling is needed I use epoxy with or without sawdust to match.
I have used hide glue as others have mentioned but more often than not will fill cracks with CA as I never have the hide glue heated up and ready when I am looking for cracks as it is before I begin any other part of assembly. For tops that I am repairing I only use hide glue as it gives the most unseen glue line.
Someone mentioned in the past on another thread but for a small batch of higher strength hide glue you can use unflavored gelatin which is about twice as strong as 192 hide glue.