Would there be anything wrong with changing a Dragonfire Adept's base breath weapon element to something other than fire? I was working on a Dragonfire Adept that was supposed to have been descended from a Silver dragon, so I thought maybe it would make more sense for Frost to be his default breath type instead of Fire with Frost as just one of the extra breath effects. Any reason to or not to do this?
Fire is the most commonly resisted type in the Monster Manual, but cold is close behind. So you're gaining a little bit out of this, unless you happen to be fighting cold immune stuff all the time.
You might have to change a couple of other minor things, like changing the Frost Breath breath effect to Fire Breath. All in all I wouldn't worry that you're breaking anything with the change, though.
I dont think there is much issues with this, unless your group disagrees.
It is true that fire is the most commonly resisted element, and is easy to find defenses against.
However, cold immunity is not all too much more rare (think all the undead).
The breath weapon is not all that overpowered anyways, so I dont think it should be a problem.
Unless you are actively abusing this or have a group that finds that unfair/unacceptable, I see no real reason to ban it, but it's "talk to your DM" thing.