I've imported 1099-B transactions.....

[nbl17]

......so now I have all the individual sale transactions.  Last year I had to mail form 8453 along with 8949.  If I were to delete the individual transactions that were imported and enter just the 8949 summary information, would that eliminate the need to mail 8453?   I got the impression that this had to be done due to the number of individual transactions.

[fanfare]

You have it backwards.

Once you itemize all the SELL details on Form 8949 and e-File there is nothing to mail.

CAUTION: TurboTax is applying its recent undocumented rules and also could be giving you that message wrongly.