So that people know what we're talking about, I quote the text of that feat from page 13 of the Yön Worldbook:
Breath Energy [Dragon]
Your can change your breath weapon to another type of energy.
Prerequisites: Dragon, breath weapon.
Benefit: You can change your breath weapon to a different energy type: either acid, cold, electricity or sonic. If you take the cold energy type, you must also take the No Flame flaw (see page 14) and your subtype changes from "fire" to "cold".
Special: You may take this feat up to four times. Each time you take it, you select a different energy type.
First, the benefit section say that you can change your breath weapon, not that you lose the previous energy type. That's why the second sentence says that if you take the cold energy type, you have to take the No Flame flaw. (There is no flaw called No Breath.) That's because you can't breathe cold and fire both, but you can have any other combination. You choose which energy to breath at the time you use the breath weapon.
I will amend the text to make this clearer for the next update. Thank you for bringing it to my attention. How about this for a description?
Breath Energy [Dragon]
Your can change your breath weapon to another type of energy.
Prerequisites: Dragon, breath weapon.
Benefit: You can select another energy type you may use as a breath weapon: either acid, cold, electricity or sonic. You choose which single energy type you emit each time you use your breath weapon. If you take the cold energy type, you must also take the No Flame flaw (see page 14) and your subtype changes from "fire" to "cold".
Special: You may take this feat up to four times. Each time you take it, you select a different energy type.
Let me know.
“You are an artist,” Yeste said.
“No. Not yet. A craftsman only. But I dream to be an artist.”
—Domingo Montoya,
The Princess Bride, William Goldman