Spirit Walk-In? Mayhap Define?
 

I'm not sure what my circumstance is called, but I was in my Linked form, or my spirit form, de-manifested and clumped together my spirit energy to go into the body of this host at the third trimester. But the baby was already clinically dead in the womb, so I re-animated it with my spirit energy and now am ... alive.

How would you define this situation? It doesn't seem to relate to your definition of a Walk-In....

I see no one seems to know the answer to your question, you actually remember your soul entering at birth? it does sound like a form of walk-in.

Do research on soul plans. Schwartz and Newton I think have books that will help explain when the soul enters the body and integrated with the baby. Usually when the baby is in the womb but some enter right at birth. They hypnotized people to find this out. Interesting reading to say the least.

I thought that the souls enters the host when the host takes first breath of air and leave the last breath of air...However another soul can enter and leave anytime it choses either to allow you to finish a task or direct you into another task of theirs or one you have to start.
But this allows us to say that a positive energy soul can enter the host as well as same as negative. Hollywood makes moves about possession of demons(negative energy) but not so much on angels ( positive energy ) needless to say you may have more than one of you inside the host or carnal human body