Walk-in is where there is an agreement between two Souls that at some stage during the incarnation where the original soul who has inhabited the body will exit and allow another soul to come in and inhabit the body. This can happen at a time of a NDE (Near Death Experience) or at a time of intense trauma. This is something which has already been agreed upon before incarnation. In some cases where a counterpart has disincarnated they can find a way back to their counterpart through a Walk-in scenario.
Soul Transference Counterpart - This is something which has become more prevalent in recent years and something which can take place in extreme circumstances where. One counterpart has delayed or opted out via free will from their soul mission. The transference of energy can go from one counterpart to another high level soulmate so that the one who is on path and purpose can continue their journey and fulfil the mission that they were set out to achieve for the purpose for Planetary Ascension.
From my understanding it is different to a walk in - The soul remains the same of the two individuals. However there is a transference of energy which is syphoned from one human body to another which initiates the ‘divine love’ frequency and ‘twin like’ qualities from one person to another so that their journey continues with two willing participants and soul mission is completed.
If the Soul Transference happened before all the lessons and learnings have been completed which happens in most cases, the transference will also transpose the relevant learning and lessons as well as the Soul Mission.