Some of the discoveries with an asterisk make sense that they are in addition to the base fire damage, but others seem like they'd replace fire damage. For instance, when an alchemist takes on an acid bomb or a frost bomb, is the acid or cold damage in addition to the original fire damage or is the elemental damage in lieu of fire damage? Alas, the discoveries don't say "in lieu" of fire damage. Help?
Bombs deal a specific amount of damage. The Frost Bomb discovery, and other such discoveries, do not change the amount of damage you deal. They just change the elemental type of that damage (and a nifty secondary effect). If the discovery actually increased the bomb's total damage, it would explicitly say by how much.
Maybe another way to think of it is that all your bomb discoveries *change* the way your default bomb works.
That's why the discoveries which change the energy type have a * next to them, because the bomb can only do one energy type at a time.
You can, however, stack any number of bomb discoveries on a bomb as long as there's only one * alteration.
So go to town with your fast, precise, smoke, strafe, frost* bombs.