"Registration Details" is a merge field that contains an overview of what was selected and includes a breakdown of the following:
  1. Unit Display Name from Get Started tab of the form
  2. Unit Price
  3. Participant Name
  4. Participant Attribute Display Name from the Field Options tab of the form
  5. Total Registration Amount

This merge field cannot be altered but if your unit information or participant attributes reference the prior year's event these can be updated on the form.