When there is no send standby clause associated with any replication definition, Replication Server sends whatever data it receives from the primary table without referring to the replication definitions.
Replication Server uses the original column names and datatypes to send data received from the Replication Agent. The replication definition is used only to find the primary key. The primary keys are the union of primary keys in all replication definitions for the table.
If schema changes do not involve dropping all primary key columns in all replication definitions of the table, the scenario is the same as one with no replication defintion. All options of alter table are supported, and no action is required in the Replication Server.
You can alter the replication definition at any point to drop all primary keys in the replication definitions, and add the new primary key columns to the replication definitions before you alter the primary table.
Drop the old primary keys only after all of the old data rows are out of the replication system. Otherwise, the Data Server Interface (DSI) shuts down. If this occurs, see for recovery instructions.