Setting Pre-Exit and post exit for standard iflow extension

Hi experts!

I have a little time with CPI UI and im having troubles with an iflow extension.

I'm working with standard iflow "Replicate Sales Order and Sales Quote from SAP Business Suite"

I have to modify a message, when currency code is "COL", it must be replace by "COP".

In another post, someone suggest me to extend the iflow because is the correct way to not lose the updates in standard iflow.

In pre-exit I dont need to change anythig so I used standard mapping "ERP_COD_CustomerOrderReplication_Preprocessing"

that uses wsdl "COD_REPLICATE_SALES_ORDER01" in input as in ouput. as shown in attached image

Theres an error when pass to the standard mapping.

"Exception:[com.sap.aii.mappingtool.tf7.rt.BehaviorInvocationException: Too many values in second queue in function useOneAsMany. It must have over all contexts the same number of values as third queue.] in class com.sap.aii.mappingtool.flib7.NodeFunctions method useOneAsMany[[Ljava.lang.String;@660c93eb,"

So I have following doubs, hope You can help me.

1. What am I doing wrong??
2. Can I just let a line between stard and end in custom pre exit iflow?
3. How can I do the post exit iflow to change the field currency code?

Regards.