No doubt about it, the rib box can expand to an increased size with pullovers and heavy breathing exercises. All experience weight trained men are aware of this. And if their not, they should be. It's the cartilage between and around the rib cage (not the rib bones themselves..that's where some confusion can come in), that has not reached a mature state, that can be encourage to stretch and expand to a greater volume. Around the ages of 22 to 24 years, the cartilage begins to lose that plastic state, becoming firmer and fixed. In which case, the potential for that expansion is reduced. But even men in their 30's and 40's (or more) have improved the ligaments/attachments around the rib box area to give a feeling of a higher lifting and fuller rib cage.
Quite a few BB'er now days focus on only the pec's for chest development. If they might re-focus that a bit to the rib box, applying some breathing pullovers with higher reps squats, they could jointly increase their gains. Taking a young BB'er with a 46" chest/pecs and adding at lease a couple more inches to at lease 48" through heavier pullovers (straight or bent arm...BB or DB) will be that much more impressive. That type pullover program will also affect the lat's very strongly. That's like icing on the cake, toward that 50" chest measurement, with time.
If your one of the lucky one's born with a deep rib box, than so much the better for you. You can have the foundation for adding to an even more impressive chest. Good Luck.