SQL Server transactional replication - behaviour of a MERGE command on the subscriber(s) vs. publisher
If you truncated the table on the publisher the record in the transaction log would be an insert, and therefor an insert would be executed against the subscriber.

Now what you can do is modify the stored procedures that replication uses at the subscriber so that when the insert procedure fires it first looks to see if the record exists and if it does it does an update, and if it doesn't it does an insert.