To discard a customized function string in a derived class and restore the function string from the parent class, drop the function string.
Use the drop function string command to remove one or more function strings in a function-string class.
When you drop the function string from a derived class, you restore the function string from the parent class.
See Replication Server Reference Manual > Replication Server Commands > drop function string.
You can also drop customized function strings from the system-provided class rs_sqlserver_function_class.
To restore a default function string for a function string with replication-definition scope that you have dropped, use the alter function string command to omit the output clause.