Yes, possible. Here's one way. "Allow Sensitive Transactions" must be a variable -- perhaps loaded from another table. It can't be part of the transactions.qvd you are loading.
Not syntax checked, but will give you the idea.
LET vCondition = if(vAllowSensitiveTransactions = 'Y',
,' ' // Allow all trans
, 'WHERE NOT match([Transaction Detail Code], 1212, 1234, 1909)'
LOAD * FROM STDQVD\TRANSACTIONS.qvd (qvd)