Many walk-ins claim meta-heightened psychic sensitivity and may take up work as New Age healers or ministers. Others claim inability to accomplish basic tasks of daily living. Clearly, at least for some, claiming a walk-in experience may have a number of secondary gains.
In classical cases, the change is immediately apparent to the subject. However, it may take weeks or months before a supposed walk-in notices, or comes to believe, that a transition has indeed occurred. The New Age religion explains this in terms of the "new soul" having enough information to take up the life of the "previous occupant" seamlessly, Occasionally, the "old self" returns after a period of months or years; whereupon either the "new self" departs, or they coexist and may try to integrate into a single being, or work out a means of cooperation and live as two persons in one body.
This kind of walk-in is very similar to old-time, pre-Sybil cases of multiple personalities such as Mary Reynolds. A period of unconsciousness is followed by the manifestation of a new self. William James studied Reynolds and Ansel Bourne, and thought of multiple personality as something natural but not yet understood, rather than a mental disease.
The Spiritualist version of the walk-in belief is similar, except that Spiritualists dealt less with "advanced beings" or guides than with the souls of ordinary persons, perhaps loved ones, who would take up residence within the body of a living person to help them or to stay in touch with earthly goings-on. An example would be the cooperative partnership of Florence Cook with "Katie King". This was regarded as a completely normal form of mediumship.
The original animus of the body is typically portrayed as spiritually exhausted, voluntarily taking a break or ceding control of the body, and the so-called new personality regarded as legitimately "in charge". While the general New Age belief about walk-ins claims represents that no soul leaves a body involuntarily, and that no soul walks into another body "without reason" or spiritual justifications, the popular understanding has evolved since its inception in 1970.
Interest in the "walk-in" phenomenon was initially stimulated in the 1970s by the popular "Seth Speaks" series of occult books written by "channel" Jane Roberts, as reputedly authored by her various "spirit-world" benefactors. In 1979, Ruth Montgomery capitalized on the fascination with Strangers Among Us, a collection of accounts of walk-ins. She included prominent historical figures among her subjects, such as Thomas Jefferson as having hosted walk-in spirits who actually wrote the Declaration of Independence.
Subsequently, a belief system grew up around the walk-in. It included New Age attributes such as the concept of "ascending into higher frequencies of evolution", a variety of psi powers, traditional "predictions regarding Earth Changes" first cited in the Book of Daniel and the Book of Revelation but popularized by Edgar Cayce, and predictions of dire fates for those whose "vibrational levels" remain unraised. In the late 1980's and early 1990's a channeling team known as "Savizar and Silarra" (Extraterrestrial Earth Mission), emphasized their "walk-in" status, claiming successive walk-in experiences together with corresponding name changes. The New Age walk-in belief system now includes a number of variant experiences such as channeling, telepathy contact with extraterrestrial intelligences, or soul merging, where the original soul is said to remain present, coexisting or integrating with the new one. As of 2006, an increasing number of people claim some type of walk-in experience.
Checklists to determine walk-in status include name changes, career changes, new interest in the study of psychic phenomena, a feeling that one is an alien, or a sudden desire to move to a new environment. Reported physical changes include memory loss and the sudden onset of allergic reactions. Since all of these factors could possibly be attributed to simple life changes such as adolescence or middle age, it's difficult to determine solely from such a checklist if a "true" walk-in has occurred. The most logical method might be to determine if any specific event historically connected with walk-ins (anaesthesia for surgery is one of the most common) occurred around the time one first started feeling differently. There is, however, no known scientific method to prove whether or not the walk-in experience has any objective reality, let alone how to determine if one has occurred.
The present belief system states that all souls come to earth in order to accomplish missions of cosmic significance, and that a walk-in is a highly evolved soul who is here to help raise the vibrational levels of humanity and doesn't want to bother with the tedious process of incarnating in the usual fashion (through birth).
Walk-ins, according to New Age teachers, are not perfect like Ascended Masters, but are invariably more spiritual, compassionate and sympathetic than the original person. This interpretation is sometimes disputed by the spouses of people who abruptly discontinue marital relations on the grounds that they are not the person whose name appears on the wedding license or that carnal love is not for those of higher vibrational frequencies. Separation, divorce, and remarriage are very common to the New Age walk-in experience.
Wikipedia - Walk-ins