Dear Rabbi Simon,
Can you send me information regarding changing the name of a child who has a severe illness through another family adopting the child. I know that that was done in the past by community rabbis. I read something about it when I was a student 15 years ago. Does my memory serve me?
I am not sure of the principle of adopting a child for the purpose of changing his or her name, however, there certainly is a tradition of changing the name of one who is ill (child or adult) as a means of warding off the Angel of Death.
The idea is that if there is a heavenly decree for a certain person to perish (eg from an illness), the change of name means that s/he is a different person, to whom the Decree does not apply. This is generally done by adding a name to the patient’s original name, thus effecting a change—rather than actually replacing the name with a different one (although this is an option). The name which is added is often one associated with healing or longevity, such as Raphael or Hayyim, or for a female, Hayya, Hava or Sarah (whose youthfulness was restored to her in her old age). The last of these is also a biblical example of one whose change of name brought about a change in her destiny—representing a biblical source for this practice.
The “change of name” is accomplished through publicly reciting a prayer for his or her recovery and using the new name at the time. It is important to actually refer to him or her using the new name in the future. When the patient recovers, the new name is used permanently.
This link contains some related information you may interesting (although the particular question to which this is a response is not identical to yours): https://www.aish.com/atr/Changing-Ones-Name.html?mobile=yes
I hope this is helpful. Best wishes for good health and all blessings.
Rabbi Rashi Simon