Yeah the "head bones" on the Minbari are actually two separate ridges that grow out and back from the temples and fuse where they meet in the middle. The "bone" itself is not actual bone but more like horn or antler and through binding and carving can be shaped into specific styles. This is why religious caste Minbari (and especially females) have a more ornate, smooth look while those of the warrior caste have a more rugged (and probably more natural) rough hewn style. It also grows more with age, hence Lennier's looking the way it does. If you look back it actually grows over the course of the show.
As for Delenn's "bone", IIRC you actually see Lennier pick of her old bone out of the remnants of the cocoon, so what she has now is all new growth.
In the real world though, yes the original make-up design did bother Mira quite a bit so when the time came for the change, they tried to make it a lot less uncomfortable to wear. Still, it took them a few episodes to figure out exactly how to handle how to wear her hair so it didn't look so odd. Regardless, I think even to this day she was never happy with how it looked.