Not sure what client you use to interact with C*. In your scenario I assume it is CQL.
So what can go wrong with TRUNCATE?
Sent: Friday, August 16, 2013 12:23 PM
Subject: Deleting column data from Cassandra without setting its TTL
What is the best way to delete column data from a Cassandra cluster after it is backed up with snapshots (using Priam or otherwise) to a stable storage?

We dont want to use the TTL option, since we would like to restore the backed-up data in the Cassandra cluster at a later time.  Setting a TTL would enable the tombstone marker, which would make it impossible to restore data.

What are the available options in Cassandra 1.2.5 in particular?