Those of you following Confessions of a Full-Time Wizard (and if you don't, you really should), are likely aware of the friendly debate waging between the author and myself—which, in no small part, involves honor, trust, betrayal, life, death, and the career choice of one slight, black-feathered fellow named Holden Cawfield.
While Holden may be crow-like in appearance (he is, you see, a kenku), his actions are more cuckoo-like in nature. The cuckoo hides its eggs in another bird's nest to be raised unwittingly. And this is how Shelly viewed Holden. He presented himself as one thing only to become another—not for his party's interests, but entirely for his own.
A little backstory to this debate: Shelly and I play in the same Scales of War campaign. A few months back, Holden auditioned for an open spot at the table, won it, and promptly joined the Wyld Stallions' as a much-needed cleric.
Then Dragon published the assassin class. Holden simply couldn’t resist.
I won't go into the intrinsic coolness of the assassin class, how I've played one since 1st Edition, or how well I feel its mechanics work in 4th Edition (though I am campaigning for a ranged assassin/sniper build). I'll only say that once the assassin appeared, I lobbied to change Holden's class, and our DM agreed.
Shelly cried fowl (last bird reference, I promise). Holden had been hired as a cleric, and—she felt—should remain one.
My defense, and the point of this editorial, goes as follows: There are, quite thankfully, a wealth of classes in this game, and a typical campaign involves sessions spanning months, if not years, of play. Many players are satisfied to run their character as originally designed for the entire length of the campaign. To them, adventuring parties resemble the Fellowship of the Ring; it just wouldn’t fit for Gimli to put down his axe or Legolas his bow and start learning to cast spells under Gandalf's tutelage. On the other hand, some players like the opportunity to sample classes. They are experimenters, dabblers, the cobblers of mechanics. Without forcing their character's death or retirement, it makes sense that they be allowed to change careers mid-campaign. There's no judgment being cast here on either style; you should play your character however you see fit, which is the heart of my argument.
Career changes happen, at the best of times, for the advancement of the character in question. Bilbo Baggins started out as a middle-aged homeowner, became a burglar, then later a traveling historian. Aragorn started as a ranger of ill-repute, only to become a field marshal, and finally king. Look at Cattie-Brie, who literally did lay down her bow to learn spellcasting. In fact, consider virtually anyone you know in the real world. I have myself worked at amusement parks, as an overnight hotel valet, delivered phone books, operated as a CIA hit man, taught English, and edited technical manuals along the course of my career.
All that said, I would not advocate career changes often or thoughtlessly. You should ask your DM's advice and permission—and you should consult your fellow players, to make sure they don't feel an important role is being vacated to the party's detriment. In Holden's case, this meant multi-classing as a cleric (of the Raven Queen, of course) and purchasing magic items to further help with healing, to soften the blow of my decision.
We often talk that the job of the DM is to make sure everyone around the table is having fun. To a large extent, the same holds true for you as the player—your job is to make sure that you're also having fun, and so contribute to the group's overall enjoyment of the game. At the most basic level, your fun begins with the character you're playing; if that character is interested in changing careers, that option should be on the table.
Just take our recent playtesting of OP's Lair Assault adventure. Afterward, Shelly herself considered a career change for her character—from Tabitha the wizard to Tabitha the barbarian.
The defense rests.