Warning bones may bend when you don't want them to.

What you need is a creature that isn't technically human to start with, it would have to have been engineered not evolved because the changes are too drastic and the pay-off is non-existent in a [natural selection](https://en.wikipedia.org/wiki/Natural_selection)/survival of the fittest environment. The alterations are quite marked and pretty extensive but if you can engineer an alt-human at all then it's rather simple because the treatment is not varied by bodily location. The whole creature simply doesn't have a solid skeleton, instead it has a lot of cartilage with bladders that it can inflate or contract when needed built into the structure, that means that it can change it's body plan to suit the situation. If the bladders are small enough and spread densely enough through the skeleton the changes can be made quite rapidly. It will owe more of it's functional anatomy to fish genetics than mammalian, although mammalian skin is thinner and more flexible so that will be easier to adapt to purpose. The heavier hair can also be stored in the skin and pushed up through channels in the dermis when needed. Such a creature need not be lupine when transformed that will depend on the neural architecture that it is paired with.