One thing that an administrator should be aware of before changing an auto-number field to text field is that this change is prevented by Salesforce; it cannot be done because it would cause data loss and inconsistency.
Auto-number fields are fields that automatically assign unique numeric values to each record; they cannot be changed to text fields because text fields do not have this functionality and may allow duplicate or invalid values. Existing field values remaining unchanged, being converted, or being deleted are not things that would happen before changing an auto-number field to text field because this change cannot happen at all.
References: https://help.salesforce.com/s/articleView?id=sf.fields_about_auto_number.htm&type=5