The Hogedep were the first known species to invent the technology using the thaumatic manipulator field, in the late 59th millennium LKY, and it is largely responsible for the diverse appearances of the Hogedep today. However, the Hogedepi respecifier was limited in how far it could reverse development, and hence changes were (literally) skin-deep. This was adequate for the aesthetic needs of the Hogedep at the time, and the technology remained stagnant until the 3rd millennium IKY, when humans became interested in the concept. Previously the Telai had experimented with non-magical means of whole-genome same-organism re-engineering, but lacking a centralized academy of sciences, efforts were limited to the abilities of a few individuals.
On Thet, respecification was initially presented (in 2792 IKY) as a means of self-improvement. Eliminating hereditary diseases was the top priority, followed by genefixed vaccinations against the few surviving parasites, such as the plague (death sand) of Illera. This was seen as a nobler use than the cosmetic alterations (used primarily for tribal and caste distinctions) of the Hogedepi antecedent.
But once the technology was widely available, its potential for more creative endeavours was hard to ignore. A large industry of gene designers and artists sprung up in the 2840s, offering both the adventurous and dull a practically limitless mode of self-expression. For a decade or two this was wildly unpopular, as society struggled with the idea that a person's body could change on a whim with (at first) a week's absence. By the late 2860s, however, the technology had become so efficient and convenient that Thessians had learned to accept the immateriality of even the most material details.
The Identity Crisis, the period from 2863 to 3261, was the result of all this. On a world of mixed cultures where many of its constituents had not eliminated the insecurities of ancient Earth, conforming to group norms was still a powerful way of ensuring one's identity. In the hands of such powerful urges, the playful experimentation of the phenotype respecifier became a channel for fashion. Trends based around emphasis of absurd features, exact duplication of a template, and everything in between fell in and out of favour.