Sorry, I did not see the declaration:

declare @Acct int = 1

Then we will just slightly modify the statement from my previous post:

DECLARE @Acct INT = 1;

MERGE @TextTable AS target

USING (SELECT Acct, (SELECT TextDesc FROM @TextTable WHERE Acct = @Acct) FROM @tempTable) AS source (Acct, TextDesc)

ON target.Acct = source.Acct

WHEN MATCHED THEN

UPDATE SET TextDesc = source.TextDesc

WHEN NOT MATCHED THEN

INSERT (Acct, TextDesc)

VALUES (source.Acct, source.TextDesc);