This process begins with storage of a creature's thought and biological patterns in specialized crystals called Therianthropic Nodes, Therianthropic Matrices if multiple are involved. This data is transformed from physical to metaphysical data as a raw form developed millennia ago by Psiolic.
From there, Therianthropists (Psiolics who study Therianthropy) will parse and transform this data into useful chunks, extricating out a creature's traits and what instincts/neurological patterns control those traits (for example, a fly's eyes and the part of their mind which translates visual data into something understandable). The more alien the part is (insect parts are further from humans than apes, for example) then the more data they'll have to keep.
Next, they will finalize programming the Node with a combination of nanotechnology and highly complex manipulation spells. The node can now perform operations in high speed (sometimes as quickly as a few moments for the most simple traits) on the person it's implanted on. The node also has a telepathic or digital interface for controlling it.
Therianthropes (Those who use the nodes) tend to keep to tried-and-true thropy developed by more qualified Therianthropists. Self-experimentation happens, but most avoid it as it's not entirely uncommon for Therianthropes to turn themselves into physical and mental abominations. Physically they may transform themselves irreversably into cronenbergian body-horrors with miserable, short-lived existences, mentally they may lose themself to the instincts and thoughts of the creatures they've attempted to merge with.
The most common branch of Therianthropy is on the creation of Thropestructs and Genestructs; these terms are nearly interchangeable but if you're being picky thropestruction relies on metaphysics and genestruction does not. In this, the Therianthropist will go through the process of creating a Therianthropic Node or Matrix, but instead of implanting it on a Sophont, they will uplift a creature to Sapient levels until it gains a soul, then use the Node to modify their behaviors and physical makeup to merge in new traits. Once these creatures reach a stable build they will be bred/manufactured en-masse to create new ecosystems for terraformation, or be sold as designer pets. Additionally they may lobotomized of all but their core function, and used as Orga tech.
On the corner of Kalipha and New Orleans St. it stood. The Hedon Villa was as much a church as a bazaar as a bathhouse as a park as a...
A trio of theriocephaly guards stood by the door, sharing a hooka among their jackal heads and puffing out plumes of smoke that changed color from one to the next. Green, blue, red, gold... The cloud covered more of their muscular, bronzed, hairless bodies than their clothing.
"Nice nuthuggers," Rohssa remarked, nodding to the leather shorts they wore. "You guys buy a matching set together or are they company supply? Do you trade them off with the next shift or-?"
"<Are you here for religion->" one cut her off, taking the hooka pipe and inhaling. The second stole it from him and continued, "<-business->", before the third took it, puffed, and exhaled a plume of cyan as he offered the pipe to them it to them, "<-or pleasure?>"
Their canid heads prevented speaking, so instead this cerberus-ian guard spoke over mind link. Their <voices> were carnal and atavistic, as though a dog had learned to speak by growling.
Rohssa plucked the proferred pipe and puffed deep. "Pleasure!~