The only way to add data to an existing table via CSV import is through the “CSV Import Block”, which is available to “Pro” subscription accounts:
When you import a CSV using the block, you can append (add) records to an already existing table. You will be able to tell the block which columns in your CSV match up to which fields in your table, to ensure the data goes into the correct fields regardless of field order in your table. It will not affect your formula fields at all.
They even updated the CSV import block recently allowing you to use it to UPDATE or MERGE records into an already existing table:
Explore the "Airtable Updates" view on Airtable.