Sorcerer Spell Selection

[Paradox]

You can still swap spells with while taking PRCs, becauae;

Spellcasting: At each level, you gain new spells per day
and an increase in caster level (and spells known, if applicable)
as if you had also gained a level in an arcane spellcasting class
to which you belonged before adding the prestige class level.
You do not, however, gain any other benefit a character of that
class would have gained. If you had more than one arcane
spellcasting class before becoming an abjurant champion, you
must decide to which class to add each level for the purpose of
determining spells per day, caster level, and spells known.

It's quite explicit that you're knowledge of spells is just like a sorcerer, ergo you can still swap spells like you're previous class.

[rubberduck]

Spellcasting: At each level, you gain new spells per day
and an increase in caster level (and spells known, if applicable)
as if you had also gained a level in an arcane spellcasting class
to which you belonged before adding the prestige class level.
You do not, however, gain any other benefit a character of that
class would have gained. If you had more than one arcane
spellcasting class before becoming an abjurant champion, you
must decide to which class to add each level for the purpose of
determining spells per day, caster level, and spells known.

it says you get your spells known and spells per day BUT nothing else doesn't it?

[The Lurker]

In any case, PH2 retraining makes it all pretty moot since it's actually better than the base spell trading mechanic.

[rubberduck]

or Psychic Reformation
but Retraining is still better since you only lose some gold

[The Lurker]

or Psychic Reformation
but Retraining is still better since you only lose some gold

Retraining costs gold?

[rubberduck]

oh wait that was the optional rule...
yeah you're right

[Paradox]

You completely missed it rubberduck,

Spellcasting: At each level, you gain new spells per day
and an increase in caster level (and spells known, if applicable)
as if you had also gained a level in an arcane spellcasting class
to which you belonged before adding the prestige class level.
You do not, however, gain any other benefit a character of that
class would have gained. If you had more than one arcane
spellcasting class before becoming an abjurant champion, you
must decide to which class to add each level for the purpose of
determining spells per day, caster level, and spells known.

I'm pretty sure swapping spell known falls under the known clause.

[JaronK]

Indeed, spells known is mentioned in there, so it should work just fine.  My DMs have all allowed it at least, and I've allowed it when I've DMed (though I've rarely DMed for Sorcerers, come to think of it).

JaronK

[The_Mad_Linguist]

If you want to really abuse the ruling, and go into total TO territory, you only "gain" spells as if you were in the previous class.  So feel free to use the trade mechanic, since the prestige class only advances your ability to gain spells, it strictly increases your spells known.  
[/silly argument 'that doesn't actually work]

If dragon material is allowed, I absolutely lurve "zap trap" as a cantrip.  It almost made it into the SPC, but got cut (they have art for it on the website).  It's basically lesser lesser electricity substituted explosive runes.