DDL replication is only supported when using Oracle.
Plus, if you look at the installation guide, page 8, of:
Non-supported objects and operations for SQL Server
Extraction or replication of DDL (data definition language) operations.
You might want to look at this doc on MOS too. It discusses how you can make the changes manually on the source and stop the Replicat on the target at the correct time to manually make the changes there.
Also, there's a new feature with EVENTACTIONS that allows you to call a shell script, so you could conceivably incorporate that into the setup to run DDL scripts on the target automatically.