Hi Tristan!
1.) The Curse is most likely to go "wrong" if a person loses his/her protective amulet. Without Kyia's direct intervention, the version of the Curse that a person gets is totally random.
2.) People choose their desired form by submitting an application form to the Citadel and then waiting for it to reach Majestrix Kyia's desk. During the wee hours of the morning, when her staff is asleep, Kyia sets aside some time to find the people whose applications have reached her and adjust the weave of the Curse around their individual bodies. Once this has been done, one of Kyia's staffers processes the forms and sends back a notification to the person that their desired version of the Curse is ready. The amulet can then be taken off (if it's the over-the-shoulders kind) or removed by a doctor (if it's an implant).
3.) There is no single Theriomorph culture. Theriomorphs, like most Keepers, are divided more by class/social status than by race or ethnicity. Within social strata, though, there are certain patterns that emerge among theriomorphs:
Nobility: The oldest and greatest noble houses of Metamor were all present in the Valley when the Curse was first laid, and struggled for years to defend the Keep against the Dark Wizard Nasoj and various other threats. Because of this, the houses have generally adopted the forms of their heroic ancestors: House Brightleaf are foxes, House Matthias are rats, and House Hassan are horses and other equines. They have to periodically "out-cross" mundane members of their families to the members of other houses, so as to preserve their genetic diversity and stave off feralism (see the notes in the wiki). The nobles are proud of their forms because they embody the memories of their honored ancestors. They may display some behavioral traits associated with their forms — the Brightleafs are known for being clever and slightly crazy, Matthiases for being crafty, bold and prolific, and Hassans for being faithful and hard-working — but for the most part they act like nobility anywhere else in the Empire.
Upper Class Commoners: The rich non-nobles generally only choose to take on the theriomorph variant Curse if they can obtain some advantage from it — e.g., a businessman might take on the Curse to attract a wife from a noble family. There isn't much of a cultural tradition of theriomorphs in this social class.
Middle Class: The theriomorph curse at the middle-class level is mostly a vehicle for social interaction. Think of the Elks Lodge or the Lions Club in our world — and then think literally. Middle-class furballs tend to play very seriously with the imagery of their chosen animals, with lots of ceremonies and weekend excursions out to the woods and the like. Once they get back to their daily lives, they generally leave the animal-related stuff back at the lodge.
Street Rats: At this level of the City, "pack mentality" becomes a very literal reality. Gangs of all types are common on the Street, and it's not uncommon for them to be modeled on wolves, lions, and other pack-hunting predators. (Bulls are also sometimes used for their strength, ferocity and purported sexual prowess, even though they're herbivores.) The pack IS the day-to-day reality for these people; they don't have a "normal life" to go home to. As a result, these tend to be the most animalistic theriomorphs in their behavior and social structure.
