It should be noted, drawing from the purely psychological and neurological perspective, that phantom experiences are at least partially guided by the nervous system sending impulses to specific portions of the body to behave in a particular way. Famously this tends to transpire in patients missing limbs, amputees, where impulses will stimulate those remaining fibers to perform some sort of function the missing limb would have been requested to do. This is why modern robotic prosthetics can engage to a large extent in the range of motion the missing limb was capable of and on some cases, new capabilities previously impossible to perform with human anatomy.
In relation to phantom changes of state, it is reasonable to associate similar expectations although, as we are all aware, this is poorly studied. It appears that because mental, sensory, and phantom shifting are all closely related and interwoven - as they would be if they manifest in reality - a similar experience of supernumerary attributes to an individual should appear. The self should, consequently, reasonably perceive a sensory mode or general addition to their person in the psyche but feel some amount of control or influence of it; conscious awareness. There is also strong grounds to propose that this experience should also be "off" and dysphoric, given the best analogy in amputees often describe the experience in tremendous and precise detail; capable of repeating the exact spacial placement of the limb or sensation and able to do things as "picture it holding a ball" or "clapping with their other hand" or "wiggling their toes in a specific pattern", but with an undertone of disbelief because they are not receiving the proper responses from impulse returns. The type of motor skills described or sensations experienced, such as with formerly sighted people who become blind as well, are as seemingly real to a trained observer as any other description minus the obvious of a physical addition.
In the case of dysphoric persons, as some psychology cases review, this appears to be part of a pervasive "offness" about their person they experience. The reports seem to propose that while the experiences are similar, they tend to be strongly perceptive - the person mostly describing what they believe it to be rather than what it is proposed to be - and that the are much less clear. It appears, or at least I will suggest it does, that the interpolation of this information, its deviation, stems from the reality that the dysphoric content adds a haziness and buffer that interferes with the interpretation and conveying of it precisely.
So for those of various typology, this is where the contention arises in relation to the claims of phantom supernumerary additions or modes. Because there is no studied model, the validity of being in this change of state, this "shift", must be measured similarly but assuming some amount of inconsistency will be present. A safe measure to make the least amount of assumptions possible, thus with the least amount of error, is to compare it as closely as to what is indeed known as described above and for the individual to test it. In theory the more accurate one is in how they feel and express it, the more plausible it is.