Quicken gave me a heart attack by erroneously renaming and categorizing a downloaded bank transaction!! The payee was 'American Eagle' (Sanitation), but Quicken decided to rename it to 'American Eagle Outfitters'!! See attachments.
Have a look at the Quicken online Help here:
https://help.quicken.com/display/WIN/Downloaded%2BTransactions%2Bpreferences
It sounds like you'll want to disable the setting for "Automatically apply Quicken's suggested name to payee".
Thank you!