Is it possible for cleric to cast spells of opposed alignments?

Question

Are there are means for clerics to cast spells with incompatible alignment descriptors?

I can think of two possibilities. The first is creating a spell that temporary switches the caster's alignment. The second is using UMD to fool the spell—but the exact wording of the UMD rules makes me skeptical that that's a valid use.

So, can I build a slippy cleric?

Small update: I search for the cheapest way to turn any outsider with the turn anathema spell. But there are other helpful usages, such as summon monster.

After reading the answer I have impression that investing skill points into UMD and having some scrolls in the equipment list would be the easiest way.

Answer 1

Yes, a cleric can UMD items of opposed alignment spells. UMD is always available for activating any item, regardless of your class or class features. This is also why a specialist wizard can use UMD to activate items from banned schools.

Doing so is still an aligned action, so doing so too often can change your alignment and put you in disfavor with your patron.

The other major option is to be in Eberron. The Eberron Campaign Setting waives the alignment restrictions on clerics.

Answer 2

(Contingent) Atonement is the nice way to do this as a player. Technically though, you're free to change alignment whenever you feel like it as not an action. That means you can be LG, decide you're CE and cast animate dead, and then be LG again. You might have grossly violated the tenets of your religion and thus lose all spellcasting powers, but you can at least get off that one Animate Dead RAW. This probably works out better for you if you are chaotic aligned.

Obligatory citation from the PHB Atonement spell description:

Note: Normally, changing alignment is up to the player. This use of atonement simply offers a believable way for a character to change his or her alignment drastically, suddenly, and definitively.

Consider taking the Craft Contingent Spell feat from the Complete Arcane and using it to build up either reserves of atonement spells set to certain conditions or just alignment specific spells set to trigger when you change to that alignment.