AFAIK you just fire up the new one and let nature take it's course :) http://www.datastax.com/docs/1.2/operations/add_replace_nodes#replace-node
i.e. you do not need to use -Dcassandra.replace_token.
Hope that helps.
Freelance Cassandra Developer
while trying out cassandra I read about the steps necessary to replace a dead node. In my test cluster I used a setup using num_tokens instead of initial_tokens. How do I replace a dead node in this scenario?