Okay let's say your a shape-shifting mythological creature who takes the place of a crooked detective in a police department's gang taskforce....
You don't have any police knowledge at least in the beginning and you also don't have any knowledge of the life of the crooked detective's life at least initially...
My question is what happens?
Oh and please could we keep any talk of gender shifting to a minimal?
Not quite relevant, because the shapeshifter MC is a police officer, but Bruce Bretthauer has a couple of shorts (Undercover Shifter and The Ted Wannabe) over on BtFH that may inspire some ideas on integration of shapeshifting with police work.
Although not relevant to shape-shifting and police work, it might be worth reading some of the better do-overs in which the protagonist gets switched into an unfamiliar body, without any of the previous incumbent's memories, then has to blag their way into the new life.
AJ
A lot depends on how much information is gathered from the target by the impostor prior or during the swap.
Even with best of preparations, what inevitably happens is quite a string of "where did you vanish?" calls as they miss preappointed meetings and traditional, routine sightings and the small near-rituals nobody notice until they change. Some will fall of with little effect, some may snowball in much trouble.
Behavior changes will be noticed, unless the swap is accompanied by prolonged observation or magic partial mind transplant, especially by significant relationships had the target had any. By close colleague too, but those are somewhat easier to explain away with having started a new relationship or something like that.
Learning the job on the fly may be lot of trouble. He will screw things up.
Depending of what the impostor's goals are, career and/or location change, temporary or permanent, may help things greatly -- by leveling the expectations, at least somewhat. Getting allies may save the day, either by full reveal or partial legend (memory loss too embarrassing to admit, something like that).
Even long time in, failing to not only recognize old acquaintances but also missing references to supposedly common memories may bring weird looks. In dealing with criminal organizations, those can be potentially deadly.
***
Long time ago I read a story where a guy met a perfect look-alike on a night train and woke up with their belongings. His own life till then wasn't great, lonely but tidy, the other guy seemed wealthy so he decided to go with the swap.
So, he found a small palace for a house, adult daughter, wife and two mistresses, one in house staff, one in the city, each with different levels of awareness of one another. He had a set of labeled gifts, but he screwed up totally the presenting of them without examining, as each of them was embarrassing and incriminating to unpack in public. Besides the crumpling palace, he had two (I think) enterprises both mired in debt and about to bankrupt.
The women unmasked him rather shortly, each in their own ways, and then helped him with the rest, and while he had to downsize things, both harem and business two years in he was about done getting it all in order just to be swapped back... I don't remember was that attempt successful.
