Import Notes to Existing Leads

If you're importing the list, creating a separate custom field as a holder of new notes may make sense - and later, you can use the trigger Person is Created with the constraint of list import - and define Change Data Value as a flow step where you concatenate original notes with new notes by using concatenated tokens -  {{Notesfield}}, {{Custom-Notesfield}}

Hope this helps,

Balkar

To ensure fields that contain existing values don't get overwritten, your best approach is to create a custom "Notes History" field (field type: text).  And then create a CDV flow step (with choice):

If NOTES is empty, NOTES-HISTORY = {{date/time}}: {{lead.NOTES}}

else

NOTES-HISTORY = {{date/time}}: {{lead.NOTES}}, {{lead.NOTES-HISTORY}}

I would create a new custom field, as Balkar said, named something like "Notes Temp" (Text type).  Import new notes into "Notes Temp" and then have a smart campaign that concatenates the "Notes Temp" and "Notes" together.

Smart list:

Trigger - Person is created

Trigger - Data Value Change > Attribute = "Notes Temp"; New Value = is not empty

Filter - Notes Temp is not empty

Flow:

Change Data Value > Attribute - Notes; New Value = {{system.date}}-{{lead.Notes Temp}} | {{lead.Notes}}